LNG Tank Research Articles

Numerical study of bund overtopping phenomena after a catastrophic tank failure using the axisymmetric approach

Hazardous materials are stored in the large tanks in the industry, e.g., a single LNG tank can be as large as 230,000 m3. Therefore, a catastrophic tank failure can cause a disastrous incident. A secondary containment, such as a bund, is required by regulations to control the risk; however, the released liquid may overtop from the bund due to its high kinetic energy converted from potential energy. Computational Fluid Dynamic (CFD) is a proper tool for the bund overtopping study, but there has been significant discrepancy among previous CFD studies. This work developed 2D CFD models of bund overtopping using the axisymmetric approach. A screening study on several turbulence models was performed, and RNG k-ε Standard Wall Functions (RNG k-ε SWF1) and Large Eddy Simulation WALE (LES WALE) were selected for a detailed comparison in terms of overtopping fraction and flow dynamic behaviour. Both RNG k-ε and LES models were systematically validated against experimental data, and the results indicate that LES model is slightly better than RNG k-ε model, and both models are acceptable based on the criteria of statistical performance measures.

Numerical study of liquid sloshing in 3D LNG tanks with unequal baffle height allocation schemes

Tank sloshing is a hotspot issue in the design of a vessel. The liquid in a partially filled tank sloshes along with the ship. Except the negative effects to the stability of the ship, the sloshing phenomena may damage the wall of the tank due to the attacking pressure. Therefore, the control of the tank sloshing is one of the researches emphasizes. While the baffles in tanks have positive effect on the control of the tank sloshing, so we compare influence of different baffle factors, such as the number of baffles, the liquid rate, excitation frequency. Then compare the effect by investigating the wave height, spectrum, hydrodynamic force and the velocity vector. The simulation processes are executed in STAR-CCM+. In the numerical simulation of the tank sloshing, we obtained a deformation at the peak of the wave height by adjusting the factors in the k−ε model, which is more approximate to the experimental results. Moreover, in order to obtain the wave height through the direct measurement of the liquid height, we derive the relationship between the liquid height and the wave height. Finally, we proposed an unequal baffle height (UBH) allocation scheme. Then compared the performance of UBH scheme with the equal baffle height (EBH) scheme which has the same baffle number under the condition that the total height of all baffles is the same. The performance of different baffle height allocation schemes are compared by setting different baffle height gradient. Numerical simulation results showed that the allocation of the baffle height has effect on the control of tank sloshing. The UBH scheme with the proper baffle height gradient performs better than the EBH scheme when we take no account of the baffle strength.

Numerical study on the horizontal stretching effect of ground on high-pressure vapor jets of LNG tank leakage

The objective of this work is to investigate the horizontal stretching effect of ground on high-pressure vapor jet of LNG tank leakage near the ground. A numerical model for leakage jet was developed and several series of leakage scenarios were theoretically analyzed for different heights of the tank orifice, inner pressures and outer temperatures. The results show that the near ground plays an important role in the horizontal transportation of LNG leakage vapor. The corresponding danger distance is surprisingly lengthened because of the horizontal stretching of leakage vapor cloud by the ground nearby, especially for those cases with a lower orifice on tank. It is illustrated that there is an obvious change for the central axis track, gas concentration and velocity of the jet in the far-field during the jet is touching the ground. In addition, the dimensionless analyses on the dependence of gas concentration, velocity and gas concentration on the transportation distance indicated that there were two stages of deflection behaviors of the jet. Finally, the enlarged danger distance by the horizontal stretching for the LNG tank leakage with a low orifice indicated the more dangerous scene of those leakage close on ground. The data and revelation here about the danger area prediction can be an important guide for the emergency management during the LNG tank leakage accidents.

Experimental investigation of the entrapped air on the hydroelasticity induced by liquid slamming under shallow-water condition

The liquid impact induced by slamming in the membrane-type tank is an important issue for the design of Floating Liquefied Natural Gas (FLNG) facilities. The free surface entrapping air may easily happen under shallow-water condition in the tank, which could result in structural local failure. Studying the effect of entrapped air on slamming load is essential to understand the air-free surface-elastic structure interaction. Thus, a series of experiments are designed and conducted in an elastic rectangular tank under shallow-water condition. The evolution of free surface and the development of entrapped air are analyzed quantitatively. Furthermore, both impact load and structural response are measured and studied in the spatial and temporal distribution under shallow-water condition. The results show that the air cavity plays a cushion role between free surface and elastic wall. Therefore, the impact mode is changed from liquid-direct impact to liquid-indirect impact. The existence of the air cavity leads to a significant reduction of the maximum slamming load and structural response but an increase in the pressure impulse in spatial distribution. It is suggested to consider the effect of the entrapped air on the determination of the slamming load for the design of super-large LNG tanks in the offshore engineering.

Development of dynamic simulation model of LNG tank and its operational strategy

Liquefied natural gas has recently received much attention due to the tightened environmental regulations associated with sulfur oxide and nitrogen oxide. LNG is generally stored in liquid form below its saturation temperature of −162 °C. During the storage process at the floating storage regasification unit, LNG continuously evaporates, and it results in the pressure build-up inside the tank leading to potential hazards unless the pressure is controlled properly. In this study, the variation in the pressure and temperature inside the storage tank was estimated by conducting a dynamic simulation of the mathematical model of a non-equilibrium LNG tank. For this, different initial filling ratios (i.e., 10, 50, and 94 vol%) were applied to the modeling and its analysis. First, the model was divided into three zones to enhance its accuracy: vapor, upper and lower LNG zones. Then, two scenarios (i.e., “sealed tank mode” and “venting mode”) were adopted for simulation. Finally, the evaporation rate of LNG was estimated based on its initial filling ratio. As a result, we could estimate the change of pressure and temperature accurately during the operation of the LNG storage and develop an operating strategy based on the different initial filling ratios.

Interoperability of LNG terminals and gas pipeline networks

The interchangeability between natural gas of different sources and LNG have been concerned and tackled to a certain extent at home, and the interconnection of gas infrastructures including LNG terminals and gas pipeline networks have also been lifted up to the national level since 2018. However, the research on the interoperability with overall-planning interchangeability and interconnection at a higher level is still in the blank stage at home. By extensively investigating EU's regulations and practices related to interoperability in the field of natural gas pipeline network, this paper put forward the conceptual definition of the interoperability of gas infrastructures including LNG terminals and gas pipeline networks for the first time. Then, the basic implementation framework and components of interoperability were set up. Finally, domestic latest typical cases which have presented the characteristics of interoperability in the recent two years were analyzed. And the following research results were obtained. First, interoperability and third-party access are two independent themes. Second, the target of interoperability is to realize the cross-system unimpeded flow of natural gas of all facility users between different facilities according to the uniform specification of specific technical standards, operation criteria and operation procedures of various facilities, based on interconnection, coordination and information interaction. Third, the framework of interoperability consists of 8 key elements, including gas quality standard & interchangeability, facility interconnection, facility interconnection agreement, unified measurement unit, unified electronic data exchange platform, technical capacity calculation method, approval procedure of LNG carrier entering the port and ship–shore compatibility unique to LNG terminals, and gas quality based LNG storage and tank loading rules. Fourth, it is recommended to give consideration to both target and requirement of interoperability and fully integrate 3 elements that are discussed more deeply and more crucial in EU countries (i.e., facility interconnection agreement, unified electronic data exchange platform and technical capacity calculation method) into the practice system of treatment reform of domestic natural gas industry chain.

Study on LNG leakage and diffusion in dangerous goods logistics park

In this paper, according to the idea of “forward model algorithm of leakage and diffusion”, the research on LNG leakage and diffusion in dangerous goods logistics park is completed, the main research contents are as follows: 1) An improved forward Gaussian diffusion model of LNG is established to modify the parameters according to the specific environment of dangerous goods logistics park. 2) The safety trace software is used to simulate the process of LNG leakage and diffusion in the hazardous materials logistics park. The applicability of the improved Gaussian diffusion model in the case of LNG tank leakage in the dangerous goods logistics park is verified by the influence of the downwind distance of the concentration contour line and environmental factors on the leakage and diffusion.

Analysis of Fire and Explosion Properties of LNG

Aim: The aim of this article is to analyse fire and explosion properties of LNG along with the identification of hazards that may arise during emergency incidents involving it. The article is based on an analysis of the available literature and a full-scale experimental study involving a 200-liter LNG tank leading to a jet fire. Introduction: Safe use and proper transport of flammable and harmful substances, together with the analysis of the effects of threats, enable the reduction of the number of accidents and provide possible conditions for the evacuation of people and property in a hazard zone. The compilation and systematization of knowledge on the safe use of the environmentally friendly LNG fuel will allow for an increase in the scope of its use. It is consistent with the state’s sustainable development policy consisting in identifying threats or adjusting technical solutions that minimize losses in transport or industry. Methodology: There are many legal acts in the world regarding safe storage and transport of LNG. One of the most important is Directive 2012/18/EC known as “Seveso III”. This document contains requirements for the prevention of major accidents involving hazardous substances – including LNG – and ways to reduce their negative effects on human health and the environment. Relevant requirements have also been specified in standards, tests, articles and other international acts, including in the European agreement on the international carriage of dangerous goods by road (the so-called ADR Agreement). The article compares flammable and explosive parameters of LNG. Possible scenarios occurring during the release and ignition of the LNG vapour cloud have been shown. The change of pressure of LNG vapour in the 200 l tank as a function of its heating time in the burning spill of a mixture of gasoline and diesel fuel is presented. In such a thermal exposure, a jet fire with a flame length of up to 5 meters was obtained. Conclusions: The proper use of flammable gases should be a priority in ensuring fire and explosion safety in facilities, during transport, etc. Hence, recognizing the threats and comparing them, or matching technical solutions that minimize the effects of LNG failures will allow active inclusion of knowledge in this field in the process of protection against fire and explosion. In case of LNG storage, attention should be paid to the types of materials in the immediate vicinity of this liquefied gas in order to have sufficient mechanical properties at the lowest liquefied gas temperature. Keywords: LNG, fire safety, process safety Article type: review article

Shortening of Construction Period and Improvement of Productivity by Application of Large-scale Precast Method in Constructing PC LNG Tanks

国内最大級（貯蔵容量230000kL）の地上式PCLNGタンクの建設に，国内で初めてプレキャスト工法を適用し，工期短縮と生産性向上を図った。より効果的な工期短縮を実現するためには，PCLNGタンクの施工特性を鑑みたプレキャスト化技術がポイントとなった。この適用に当たっては，事前にプレキャスト版接合部の確認試験・モックアップ試験等を行い，性能や施工手順・歩掛りを確認した。工事に適用した結果，全体工期を従来工法で約40カ月のところ29カ月に短縮し，現場で従事する建設技能工を従来工法に比べて40％削減することができた。

Influence the Filler Metal Containing Zirconium on the Weld Metal Porosity of The MIG Welded Aluminum Alloy 5083

The aluminum alloy series 5083 has high corrosion resistance and high specific strength properties; hence, it is widely used for ship structures, marine components, cryogenics of LNG tanks, and unfired pressure vessels. This study was undertaken to investigate the effect of zirconium on weld metal porosity and hardness of MIG welded aluminum Alloy 5083. Zirconium is one of the alloying elements that are mostly used for grain refining in the aluminum casting process. Zirconium element was previously added in the electrode wire as a filler metal. The experiments were carried out by MIG welding for several aluminum alloy plates to produce the full penetration weldments. Two different filler wires used in the welding: one is containing zirconium, and another is no containing zirconium. The grain size of weld microstructures was measured using a Linear Intercept Method (ASTM E 112), and the hardness measurement is conducted using micro-Vickers along the cross section of AA-5083 weldment. Results showed that the grain size of AA-5083 weldment using the filler metal containing zirconium was considerably finer size than that of using the filler metal without zirconium. Moreover, the hardness of AA-5083 weldment using the filler metal containing zirconium is generally higher than that of using the filler metal without zirconium.

Analysis of the Effect of Sloshing on Damage Stability after the Addition of LNG Tanks

The Damage Stability, better known as leaky ship stability, is a condition where the vessel has a leak in the ship's compartment so that the stability condition of the ship is disrupted. This study is a study of the effects caused by sloshing on the stability of the ship. The method used to calculate damage stability is the lost buoyancy method. This method assumes a condition where when the vessel has a leak, the vessel buoyancy will decrease. This happens because the empty space in the vessel will be filled with water, so it is no longer the part that contributes to the buoyancy so that the ship will increase and can result in sinkage. According to the calculation of SOLAS (Safety of Life at Sea) Consolidated Edition 2014 Chapter II-1 Part B-1. There are two indexes compared, namely index Required index R = 0.77172, which depends on the length of the lining and Attained subdivision index A = 0.83736. The pi factor shows a maximum of 5 leak zones that can be overcome by the ship to remain stable. By comparing the index value of A> R, it can be seen that this ship has fulfilled the SOLAS requirements .

Strength analysis of LNG tank container for trains under inertial force

As transportable pressure vessel, LNG tank container used in trains bears not only the static load, but also inertial load during transportation. The finite element method is commonly used in the design of tank containers subjected to inertial force. In this paper, a finite element model for 1AA LNG tank container was established using the ANSYS software, stress analysis and strength assessment under five load cases were performed for the tank container. The results show that the Mises equivalent membrane stress at the frame is controlled by the inertial force but at the inner vessel, however, it depends on the internal pressure although it may be significantly affected by the inertial force in some cases.

Predicting saturated vapor pressure of LNG from density and temperature data with a view to improving tank pressure management

Determining the saturated vapor pressure (SVP) of LNG requires detailed thermodynamic calculations based on compositional data. Yet LNG compositions and SVPs evolve constantly for LNG stored in tanks. Moreover, the SVP of the LNG in a tank influences boil-off rates and tank pressure trends. In order to make improved tank pressure control decisions it would be beneficial for LNG tank operators to be made more constantly aware of the SVP of the LNG in a tank. Machine learning models that accurately estimate LNG SVP from density and temperature inputs offer the potential to provide such information. A dataset of five distinct, internationally traded LNG cargoes is compiled with 305 data records representing a range of temperature and density conditions. This can be used graphically to interpolate LNG SVP. However, two machine learning methods are applied to this dataset to automate the SVP predictions. A simple multi-layer perceptron artificial neural network (MLP-ANN) predicts SVP of the dataset with root mean square error (RMSE) = 6.34 kPaA and R2 = 0.975. The transparent open-box learning network (TOB), a regression-free optimized data matching algorithm predicts SVP of the dataset with RMSE = 0.59 kPaA and R2 = 0.999. When applied to infill unknown LNG compositions the superior TOB method achieves prediction accuracy of RMSE ∼3kPaA and R2 = 0.996. Predicting LNG SVP to this level of accuracy is beneficial for tank-pressure management decision making.

Zero methane loss in reliquefaction of boil-off gas in liquefied natural gas carrier ships by using packed bed distillation in reverse Brayton system

Reverse Brayton refrigeration cycle with nitrogen as working fluid is widely used in reliquefaction of boil-off gas generated in LNG tanks onboard. These reliquefiers allow venting of some vapour that has methane in it. This entails a loss of energy and release of greenhouse gas into the environment. As the boil-off gas contains low-boiling temperature nitrogen, its complete reliquefaction is possible only by decreasing the pressure at the turbine outlet that makes the reliquefaction system bulkier. In this paper, two proposed modifications have succeeded in achieving zero methane loss without any reduction of turbine outlet pressure. In one modification, the vent gas is recycled and completely reliquefied with the boil-off gas. In other modification, a distillation column purifies the vent gas to less than a part per million of methane in it and near-pure nitrogen is fed back to the system. Rational exergy efficiency of vent-recycled and distillation column systems are higher than the basic system by 14.9% and 8.7% respectively albeit with some increase in mass flow rate of nitrogen compressor and the size of heat exchangers. The period of return on investment reduces by one month and increases by six months in vent-recycled and column system respectively.

Suppression of hydrodynamic sloshing in liquefied natural gas tank with floating baffle: Experimental and numerical studies

A fixed anti-sloshing mechanism such as baffles which modifies the tank structure may lead to increment of the maintenance cost. This paper proposes a floating baffle, and reviews its investigation on the sloshing behaviour in a membrane-type tank model under unidirectional excitation with 30% and 50% of filling ratio. An LNG tank was numerically simulated in OpenFOAM under regular sinusoidal motion with an amplitude of 3 cm and excitation frequency set to the natural frequency at 1.1 seconds. Impulsive pressure on the tank wall was obtained, and then benchmarked with the experimental results from the pressure sensors. The simulation and experiment results showed an acceptable agreement with a root mean squared error of less than 10%. The findings are expected to become a significant reference for safer sea transportations such as conventional LNG vessels.

LNG Tank Sloshing Simulation of Multidegree Motions Based on Modified 3D MPS Method

Modified 3D Moving Particle Semi-Implicit (MPS) method is used to complete the numerical simulation of the fluid sloshing in LNG tank under multidegree excitation motion, which is compared with the results of experiments and 2D calculations obtained by other scholars to verify the reliability. The cubic spline kernel functions used in Smoothed Particle Hydrodynamics (SPH) method are adopted to reduce the deviation caused by consecutive two times weighted average calculations; the boundary conditions and the determination of free surface particles are modified to improve the computational stability and accuracy of 3D calculation. The tank is under forced multidegree excitation motion to simulate the real conditions of LNG ships, the pressures and the free surfaces at different times are given to verify the accuracy of 3D simulation, and the free surface and the splashed particles can be simulated more exactly.

Laterally Loading Experimental Study of Bearing Capacity Characteristics of Large-Diameter Bored Cast-in situ Deep and Long Pile

Base on the laterally static load and pile stress testing results of three kinds of different construction technology piles (post-grouting pile, expanded branches and bells by 3-way extruding arms, squeezed branch piles) in Tangshan LNG tank area, the distribution law of pile top deformation, moment and shear was analyzed under laterally load. The test results showed that: The H–Y0 curves of three different construction technology piles have no significantly the inflection point and have same deformation law; H–△Y0/△H curve show three stage: elastic stage, elastic–plastic stage and failure stage. The critical load value and ultimate load value of three different construction technology piles is same; The distribution rule of three piles’ moment increases firstly and then decreases with the pile depth, the support plate (fork) that is set the lower pile position has little effect of the top pile load and the bending moment; The relationship of foundation soil horizontal resistance force’s ratio coefficient (m) versus laterally load and pile top displacement are nonlinear, the curve of m and mud surface displacement (Y0) is fitted by exponential equation and m value corresponding to pile top displacement is gained, the design basis is provided for engineering design.

Study on sloshing simulation in the independent tank for an ice-breaking LNG carrier

As the LNG carrier operates in ice covered waters, it is key to ensure the overall safety, which is related to the coupling effect of ice-breaking process and internal liquid sloshing. This paper focuses on the sloshing simulation of the ice-breaking LNG carrier, and the numerical method is proposed using Circumferential Crack Method (CCM) and Volume of Vluid (VOF) with two main key factors (velocity vx and force Fx). The ship motion analysis is carried out by CCM when the ship navigates in the ice-covered waters with a constant propulsion power. The velocity vx is gained, which is the initial excitation condition for the calculation of internal sloshing force Fx. Then, the ship motion is modified based on iterative computations under the union action of ice-breaking force and liquid sloshing load. The sloshing simulation under the LNG tank is studied with the modified ship motion. Moreover, an ice-breaking LNG ship with three-leaf type tank is used for case study. The internal LNG sloshing is simulated with three different liquid heights, including free surface shape and sloshing pressure distribution at a given moment, pressure curves at monitoring points on the bulkhead. This present method is effective to solve the sloshing simulation during ice-breaking process, which could be a good reference for the design of the polar ice-breaking LNG carrier.

Development and investigation of means of transportation, storage, gasification and refueling of cryogen liquids of space systems

The paper describes the development of hydrogen, oxygen, LNG (tank cars, container cars) stationary devices based on the existing constructions. The investigation results of liquid hydrogen losses on experimental cryogenic storage and transport tanks with different thermal insulation (multilayer-vacuum, powder-vacuum, screen-vacuum (with a nitrogen screen of different designs)) are presented. The paper presents the results of research on obtaining and maintaining pressure in the tank of a gasification plant with hydrogen supercritical parameters for long-term product delivery to the customer at variable or constant flowrate, both using an external source of hydrogen and a part of the hydrogen supplied to the consumer as a heat carrier. The paper presents a method and equipment of refueling the Orbiter fuel tanks with high-purity hydrogen for variable hydrogen mass and different number of tanks.

Mutual effects between dynamic leakage behavior and the pressure/temperature in a LNG tank with external heat fluxes

The objective of this work is to investigate and model the mutual effects between the dynamic pressure/temperature in the LNG tank and the leakage behavior with external heat fluxes. The results suggest that the pressure and temperature in tank during leakage change with the comparison results between the heat flux consumed in liquid boil-off and the external heat flux supplied. At the liquid leakage stage, when the external heat flux is not very high, the pressure in tank tends to increase significantly, even results in tank explosion. It increases more and more heavily with higher and higher external heat fluxes. At the vapor leakage stage, large amount of vapor spray out, which results in a high generation rate of vapor by the liquid boil-off. The pressure in tank normally decreases to be low, which is unfavorable for the LNG tank explosion. Therefore, at this vapor leakage stage, blocking the leakage hole as soon as possible is not always a right choice for fire fighters. Finally, it is suggested that reducing the heat flux into the tank, either at the liquid leakage stage or in vapor one, is key to the tank safety.