Liquefied Natural Gas Tank Research Articles

Trajectory planning and automatic docking of LNG five-axis loading arm

PurposeIn response to the challenges posed by the conventional manual flange docking method in the LNG (Liquefied Natural Gas) loading process, such as low positioning accuracy, constraints on production efficiency and safety hazards, this study analyzed the LNG five-axis loading arm’s main functions and structural characteristics.Design/methodology/approachAn automated solution for the joints of the LNG loading arm was designed. The forward kinematic model of the LNG loading arm was established using the Denavit–Hartenberg (D-H) parameter method, and its workspace was analyzed. The Newton–Raphson iteration method was employed to solve the inverse kinematics of the LNG loading arm, facilitating trajectory planning. The relationship between the target position and the joint variables was established to verify the stability of the arm’s motion. Flange center identification was achieved using the Hough transform function. Based on the ROS platform, combined with Gazebo and Rviz, an experimental simulation of automatic docking of the LNG loading arm was conducted.FindingsThe docking errors in the XYZ directions were all less than 0.8 mm, meeting the required docking accuracy. Moreover, the motion performance of the loading arm during docking was smooth and free of abrupt changes, validating its capability to accomplish the automatic docking task.Originality/valueThe proposed trajectory planning and automatic docking scheme can be used for the rapid filling of LNG filling arms and LNG tankers to improve the efficiency of LNG transportation. In guiding the docking, the proposed automatic docking scheme is an accurate and efficient way to improve safety.

Quantitative Risk Assessment of an Oil-Gas-Hydrogen-Electricity Integrated Energy Station in China.

This paper presents a quantitative risk assessment (QRA) study of an oil-gas-hydrogen-electricity integrated energy station in China. A comprehensive assessment of the station was made in terms of consequences and risks, respectively. Consequence analysis shows that the severity of hazardous chemical leakage accidents in the station is in the order of natural gas, hydrogen, gasoline, and diesel fuel, especially in the liquefied natural gas (LNG) and compressed natural gas (CNG) storage tank areas, which may cause major accidents in the event of leakage. The results of the risk assessment showed that the individual and societal risks of the integrated oil-gas-hydrogen-electricity energy station exceeded the risk acceptance criteria. Moreover, the catastrophic rupture of LNG and CNG storage tanks is the main cause of the unacceptable risk. Additional mitigation measures for them, mainly including the installation of emergency manual shut-off valves, the installation of combustible gas detection and alarm devices, and pressure relief protection devices, can effectively reduce the risk to an acceptable level.

Full-scale tests of a long energy pile subjected to separated and coupled thermo-mechanical loads

In this paper, four individual full-scale tests were carried out to study the mechanical response of a cast-in-place energy pile beneath a liquefied natural gas (LNG) tank subjected to separated and coupled thermo-mechanical loads. The results show that the temperature profiles displayed a comparable trend in response to pile heating, cooling and recovery. Specifically, the temperature at the mid-depth of the pile fluctuated rapidly, while the changes at both ends were relatively slower. During the thermal stages, when the pile had the flexibility to expand or contract, the observed strain at the pile head significantly deviated from the free thermal strain. In contrast, the strain at the pile toe was relatively aligned with the free thermal strain. The thermally induced stress obtained at the end of the coupled loading–cooling stage was found to exceed the tensile strength of the C40 reinforced concrete. However, under the actual testing conditions, both the settlement and the bearing capacity of the pile remained well within the required values, ensuring the structure of the LNG tank will not be damaged.

Seismic performance of LNG tanks in deep soil site considering soil-foundation-structure interaction

The seismic performance of liquefied natural gas (LNG) tanks is significantly influenced by Soil-Foundation-Structure Interaction (SFSI). It is essential to investigate the effect of the SFSI on isolated LNG tank, particularly on a deep soil site. This study aims to examine the impact of the SFSI on the seismic performance of an isolated LNG tank located on the deep soil site. The impact of foundation type, pile length, and the frequency content on the primary seismic responses of the LNG tank were thoroughly examined in this study. These seismic responses include the acceleration of the outer tank, the height of the sloshing wave, and the shear force and bending moment of the inner tank. Additionally, the seismic force along the pile foundation, such as shear force, lateral displacement, and bending moment, was also analyzed. The results indicate that for isolated LNG tanks, it would be dangerous without considering the SFSI, while for the pile foundation, it may be beneficial when considering the SFSI. The pile foundation types did not considerably affect the seismic response of the isolated LNG tank in the deep soil site. Additionally, the seismic response appears to be highly sensitive to the frequency characteristics of the seismic excitation, especially the low-frequency content.

Analysis of seismic response of a large-scale isolated LNG tank considering dynamic soil-pile interaction

Seismic safety is a critical issue for liquefied natural gas (LNG) tanks. It is essential to investigate the effect of the isolation system on the seismic response of LNG tanks, considering dynamic soil-pile interaction, especially for tanks located in the deep soil site. This study aims to quantitatively evaluate the effects of isolation system (e.g., lead-core rubber bearings) on various aspects of a large LNG tank located on a deep soil site under horizontal bi-directional seismic action. Specifically, the evaluation includes outer tank acceleration, inner tank base shear, overturning moment, and pile force distribution. The findings demonstrate that the isolation system can effectively minimize the transfer of inertial interaction from the superstructure to the pile foundation, optimize the internal force distribution within the pile foundation, mitigate the pile group effect, and enhance the safety margin of the structure. Moreover, the isolation system can effectively suppress the transmission of seismic energy in medium and high frequencies, but amplify it in the low-frequency domain. Consequently, it is recommended that it is needed to avoid the site's natural frequency in the design of seismic isolation bearings for LNG tanks.

Nelinearno ponašanje spremnika za ukapljeni prirodni plin s različitim sustavima potresne izolacije

This study determines the effects of different types of base isolator systems on the seismic performance of liquefied natural gas (LNG) storage tanks. Nonlinear time-history analyses of the non-isolated and three different isolated models were performed for the average acceleration of seven ground motions scaled to achieve a specified safe shutdown earthquake. The ANSYS Workbench program was used in the modelling studies of the LNG liquid, inner steel tank, outer shell, ring beam, roof and concrete foundation and side wall insulation. The LS-DYNA program was used for the nonlinear analyses of the LNG liquid, inner steel tank and concrete foundation. The results of the total base shear force, sloshing height, steel tank stresses and lateral deflection were compared. The results indicated that there was no difference between the convective and impulsive modes for the LNG tanks with isolators. It was concluded that the wave motion of the liquid was different from the oscillation of the structure and the earthquake isolation times did not affect the sloshing motion. In the non-isolated system, the stress reached 400 MPa, whereas it was 350 MPa on average in the LNG tanks with isolators.

Boil-off gas precooling process for subsea low temperature LNG pipelines

Moving liquefied natural gas (LNG) ports offshore and transporting LNG to the coast through submarine pipelines can address the required water depth for LNG tankers and prevent potential safety hazards at ports in crowded waterways. At ultra-low LNG temperatures (−160 °C), pipelines should be precooled by LNG boil-off gas (−120 °C) before normal operation to avoid instantaneous LNG gasification and sharp pipe contraction. In the present study, a transient mathematical model was developed for the precooling process in a subsea multilayered LNG pipeline. Heat conductivity varied with temperature, and the governing equations were solved using the finite difference method. Additionally, the effects of pipe size, insulation layer thickness, and insulation material were investigated. The precooling time decreased significantly with increasing pipe size, and a pipe diameter in the range of 30” to 40” was suitable. In terms of economy and practical applications, the thickness of the insulation layer was suggested to be 30–60 mm. Moreover, compared with glass foam insulating material, rigid polyurethane foam exhibited better thermal performance during the precooling process. These results can assist in determining a safe precooling process for subsea LNG pipelines, providing a suitable green alternative to fossil fuels.

A multi-zone thermodynamic model for predicting LNG ageing in large cryogenic tanks

During the storage and transportation of liquefied natural gas (LNG), generation of boiloff gas (BOG) and change in the LNG composition, also known as LNG aging, are inevitable. Thus, a thermodynamic model that can accurately predict LNG aging during long-term operation is critical. This study presents a novel aging model, in which the LNG tank is divided into five zones: the vapor phase region, thermal stratification, bulk liquid region, boundary layer, and surrounding thermal insulation region. The heat and mass transport into different regions were calculated separately, and the thermal conductivity of the solid walls was considered as a function of temperature. Following model validation, simulations were performed for various thermal insulation conditions, ambient temperatures, and initial liquid compositions. From the results, the errors of the pressure, BOG rate and total heat flux could be approximated to 17, 7, and 14% respectively, for the previous models omitting the variation of thermal conductivity with temperature. As the initial methane fraction increased (i.e., N fraction decreases), the BOG rate decreased at the initial stage, while the BOG rate became less sensitive with the initial LNG composition as evaporation proceeded. Such an effect is determined by the variation in the latent heat of vaporization and total heat loss. This study can provide guidance for the design and operation of LNG storage tanks.

Numerical study on the effects of bund on liquid pool spreading and vapor dispersion after a catastrophic LNG tank failure

Liquefied natural gas (LNG) storage tanks are usually equipped with bunds to provide an additional layer of protection. However, the catastrophic failure of an LNG storage tank usually results in a bund overtopping. The overtopped LNG will evaporate rapidly at ground surface to form the flammable gas cloud. Previous studies have developed computational fluid dynamics (CFD) models to investigate the ability of bunds to retain liquids; However, the models were developed based on ambient liquid, ignoring the evaporation phenomena and vapor dispersion of LNG. In this work, a multiphase CFD model which integrated with the evaporation model was proposed to simulate the complete overtopping process (including LNG overtopping, LNG spread, LNG evaporation and vapor dispersion). The data from two field experiments were used to validate the model. In addition, this paper studied a case of catastrophic failure that derived from an industrial LNG Tank. The effect of the bund configurations on the wind flow field, the overtopping fraction, the spread of LNG and the dispersion of LNG vapor cloud was analyzed. The present work can help relevant personnel to better assess the engineering risks associated with catastrophic failure of storage tanks for decision making in the process safety framework.

“Ship-port-country” multi-dimensional research on the fine analysis of China's LNG trade

Liquefied Natural Gas (LNG) is a clean and low-carbon energy source that plays an important role in combating global warming. As the world's largest greenhouse gas (GHG) emitter, China has taken coal-to-gas as an important measure to reduce GHG emissions, and has become the world's largest LNG importer. Studying the patterns and characteristics of China's LNG trade is of great significance for ensuring energy supply security, formulating and adjusting energy strategies. However, the refined analysis of China's LNG trade is still inadequate, mainly due to the lack of research on the details of ship trajectories and port attributes. Therefore, a “ship-port-country” multidimensional LNG trade analysis method is proposed to improve the timeliness, multi-dimensionality and fineness of China's LNG trade analysis. The multidimensional characteristics of China's LNG trade are analyzed by studying the big data of nearly 3.5 billion automatic identification system (AIS) records in 2017. The study has found that (1) The arrival frequency of China's LNG trading ships varies greatly with time. For example, the most frequent daily arrivals are between 04:00 and 05:00 in the morning, while the least frequent arrivals are between 15:00 and 17:00 in the afternoon. (2) The Chinese LNG trade network consisting of 79 ports has been formed, of which NANTONG Port is the most important port. (3) The LNG trade volume calculated in this study has shown a strong correlation with the national LNG trade statistics and can be used to analyze LNG trade with higher spatial and temporal resolution. According to the characteristics of LNG trade at the three levels of ship, port and country, China can optimize its LNG trade policy from the following aspects: (1) Dynamically allocate port resources according to the arrival frequency of LNG tankers to reduce port congestion and waste of resources. (2) Expand core LNG trading ports such as NANTONG Port, ZHOUSHAN Port, TANGSHAN (JINGTANG) Port, XIUYU Port, DALIAN Port and LUSHUN Port. (3) Actively realize the diversification of LNG trading partners to reduce the dependence of LNG import sources on one country or region, and ensure energy security. The “ship-port-country” multi-level LNG trade analysis method proposed in this study provides a new research perspective for the analysis of the LNG trade pattern. This study reveals the multidimensional characteristics of China's LNG trade, which can provide decision-making support for China to formulate reasonable LNG trade policies and energy security policies, and is conducive to the stable and sustainable development of global LNG trade.

Experimental Determination of the Flow Coefficient for a Constrictor Nozzle with a Critical Outflow of Gas

Reduction of energy expenditures required for various technological processes is a pressing issue in today’s economy. One of the ways to solve this issue in regard to liquefied natural gas (LNG) storage is the recovery of its vapours from LNG tanks using an ejector system. In that respect, studies on the outflow of the real gas through the nozzle, the main element of the ejector, and identifying differences from the ideal gas outflow, are of high relevance. Particularly, this concerns the determination of the discharge coefficient µ as the ratio of the actual flowrate to the ideal one, taking into account the energy losses at gas outflow through the nozzle. The discharge coefficient values determined to date for various nozzle geometries are, as a rule, evaluated empirically and contradictory in some cases. The authors suggest determining the discharge coefficient by means of an experiment. This paper includes µ values determined using this method for the critical outflow of air to atmosphere through constrictor nozzles with different outlet diameters (0.003 m; 0.004 m; 0.005 m) in the pressure range at the nozzle inlet of 0.5–0.9 MPa. The obtained results may be used for the design of an ejector system for the recovery of the boil-off gas from LNG tanks, as well as in other fields of industry, for the design of technical and experimental devices with nozzles for various applications.

Research on digital twin based temperature field monitoring system for LNG storage tanks

The temperature distribution is a critical indicator of the health condition of liquefied natural gas (LNG) storage tanks. Point measurements are the main method of traditional LNG tank temperature field monitoring. To obtain more abundant temperature data and realize the digital transformation of temperature field monitoring, an LNG tank temperature field monitoring system was constructed, which consists of a model layer, a data layer, and an application layer, by combining sensing data with digital twin (DT) technology. First, the temperature distribution of the LNG storage tank under working and leaking conditions was simulated, and the sensing monitoring network was constructed by combining Fiber Bragg Grating (FBG) sensor temperature-sensing experiments. Second, a finite element calculation model of the steady-state temperature field of an LNG storage tank was developed, and the twin model was generated by fusing the sensing data to realize the inversion from local sensing data to the whole temperature field. Finally, an LNG temperature field monitoring system based on the DT was constructed. Based on physical field leakage simulations performed with the Fluent software, the functions of visual interaction, construction splitting, temperature chart analysis, leakage diagnosis, and historical data management of the twin models were realized, which provided system building samples for digital monitoring of new LNG storage tanks.

Aerogel Technology for Thermal Insulation of Cryogenic Tanks—Numerical Analysis for Comparison with Traditional Insulating Materials

The traditional choice of insulation material for liquefied natural gas (LNG) transportation with cryogenic tankers is the back-filled perlite-based system. However, aiming to further cut down the insulation cost, spare additional arrangement space, and provide safety in installation and maintenance, the requirement of looking for alternative materials still exists. Fiber-reinforced aerogel blankets (FRABs) could represent good candidates in designing insulation layers for LNG cryogenic storage because of their ability to ensure adequate thermal performance without the need to create deep vacuum conditions in the annular space of the tank. In this work, a finite element method (FEM) model was developed to study the thermal insulation performance of a commercial FRAB (Cryogel ® Z) for application in cryogenic storage/transport LNG tanks, comparing it with the performance of traditional perlite-based systems. Within the reliability limits of the computational model, the analysis proved that FRAB insulation technology gave encouraging results and might be potentially scalable for transporting cryogenic liquid. In addition to demonstrating superior performance in terms of thermal insulating efficiency and boil-off rate over the perlite-based system, as far as a perspective of cost savings and space gain, FRAB technology allows for higher levels of insulation without vacuum and with lower thickness of the outer shell, which is therefore beneficial for storing more material and lightening the weight of the LNG transportation semitrailer.

Random Fatigue Analysis of Cryogenic Liquid Tanker Under Road Spectrum Load and a Simplified Algorithm

AbstractThe lightweight of liquefied natural gas (LNG) tanker can reduce transportation cost and improve transportation efficiency. However, in lightweight design, the random vibration analysis based on fluid–structure interaction (FSI) is difficult, which demands to be effectively solved by simplifying the finite element model and load. The vibration test and fluid–structure interaction modal numerical analysis of a tanker model were carried out, respectively, and the results are in good agreement. Taking the DC18 LNG tanker as an example, the random vibration response analysis was carried out based on the fluid–structure interaction modal numerical analysis, and the random fatigue damage coefficient of the support region of the inner container was obtained, which was used as the benchmark for the model and load simplification. The finite element model of the LNG tanker was simplified by applying the equivalent liquid mass to the walls of the inner container in the form of density. It is found that when the equivalent liquid mass ratio is 40%, the random vibration response characteristics of the DC18 LNG tanker are close to the actual structure. In the static calculation of the simplified model, the stress response of the container support area is close to the actual structural when the equivalent road spectrum load is 0.95 g vertical acceleration. In this case, the stress result and the overall damage coefficient equivalent to the actual structure can be obtained just by static calculation, which greatly simplifies the solution process.

Fatigue Analysis of a 40 ft LNG ISO Tank Container.

The demand for Liquefied natural gas (LNG) has rapidly increased over the past few years. This is because of increasingly stringent environmental regulations to curb harmful emissions from fossil fuels. LNG is one of the clean energy sources that has attracted a great deal of research. In the Republic of Korea, the use of LNG has been implemented in various sectors, including public transport buses, domestic applications, power generation, and in huge marine engines. Therefore, a proper, flexible, and safe transport system should be put in place to meet the high demand. In this work, finite element analysis (FEA) was performed on a domestically developed 40 ft ISO LNG tank using Ansys Mechanical software under low- and high-cycle conditions. The results showed that the fatigue damage factor for all the test cases was much lower than 1. The maximum principal stress generated in the 40 ft LNG ISO tank container did not exceed the yield strength of the calculated material (carbon steel). Maximum principal stress of 123.2 MPa and 107.61 MPa was obtained with low-cycle and high-cycle analysis, respectively, which is 50.28% less than the yield strength of carbon steel. The total number of cycles was greater than the total number of design cycles, and the 40 ft LNG ISO tank container was satisfied with a fatigue life of 20 years.

Quantitative risk assessment on loading and unloading ships exclusively carrying LNG tank containers

Quantitative risk assessment (QRA) on protocol that allows maximum 96 40ft heavy LNG containers carried by a single ship in a dock was performed using applications EFFECTS and RISKCURVES, to investigate the hazard while loading and unloading ships exclusively carrying liquefied natural gas (LNG) tank containers in a dock. Through analyzing typical accident scenarios, the simulation predicted the range of the accident impact. Individual and social risk levels during loading and unloading were calculated to determine the hazard level while loading and unloading ships exclusively carrying LNG tank containers. The results show that the individual and social risk levels while loading and unloading ships exclusively carrying LNG tank containers are acceptable and meet the requirement of existing regulations.

Quantitative risk assessment on loading and unloading ships exclusively carrying LNG tank containers

Quantitative risk assessment (QRA) on protocol that allows maximum 96 40ft heavy LNG containers carried by a single ship in a dock was performed using applications EFFECTS and RISKCURVES, to investigate the hazard while loading and unloading ships exclusively carrying liquefied natural gas (LNG) tank containers in a dock. Through analyzing typical accident scenarios, the simulation predicted the range of the accident impact. Individual and social risk levels during loading and unloading were calculated to determine the hazard level while loading and unloading ships exclusively carrying LNG tank containers. The results show that the individual and social risk levels while loading and unloading ships exclusively carrying LNG tank containers are acceptable and meet the requirement of existing regulations.

Turbulence analysis for vertical baffle configurations on prismatic tanks by the MPS method

A series of conceptual baffles have been proposed to attenuate pressure effects provoked by sloshing on the walls of Liquefied Natural Gas (LNG) tanks. However, these structures provoke turbulent behavior that need to be analyzed to avoid non-desired fluid effects. In this work, numerical sloshing analyses are developed by a two dimensional Moving Particle Semi-implicit (MPS) method applying the Sub-Particle-Scale Large Eddy Simulation (SPS-LES) turbulent model to identify the turbulent effects due to global motions on a prismatic LNG tank for two filling fractions. The impact pressure, total force, and total moment on tank walls are compared to a prismatic tank without baffles, one configuration with one baffle and two configurations with two baffles. The results illustrate the turbulence effects generated by the three baffle configurations on partially filled tanks (25% and 50% of filling fraction) showing that the effect of the baffles to reduce sloshing effects is more significant for low filling levels (25% of filling fraction), and also, there is a small difference on the sloshing reduced effects between one baffle or two baffles at different separations. However, important turbulent effects appear for high filling levels (50% of filling fraction) specially at roll motion.

Transient performance study of high pressure fuel gas supply system for LNG fueled ships

The transient performance of the fuel system is a critical issue for the operation of liquefied natural gas (LNG) fueled ships. In this paper, experiments and simulations of a high pressure fuel gas supply system (HP-FGSS) were conducted to investigate the system transient responses during load variations and environmental disturbances. A prototype of the HP-FGSS was tested at different running loads from 0% to 110% in combination with a MAN high pressure two-stroke dual fuel engine. A dynamic model of the HP-FGSS was developed and validated by the test data. The effects of the operating parameters and equipment sizes on the system performances were simulated and analyzed. The results show that during the load variations from 75% to 100% the fuel gas pressure fluctuation is nearly 10 bar and lasts for 5 min. The HP-FGSS control system has a high robustness to the LNG composition, but the pressure overshoot increases as the methane content decreases. The LNG composition will also affect the steady state value of the gas temperature. The buffer tank volume has a significant impact on the pressure response. The pressure disturbance in the LNG tank induced by violent sloshing will be transmitted to the suction port of the high pressure pump, causing a cavitation risk.

The selection of Sufficiently Efficient ISO LNG Tanks for Applications in Industrial Estates based on Edward Lisowski and Wojciech Czyzycki

Liquefied Natural Gas (LNG) is more likely to employ gasoline in street transportation applications because of its greater cryogenic energy density as a result, the key problem with this technology is the tank mounted on board with the control system and vaporizer board required to give the internal combustion engine (ICE) input. The research approach employed in this study was quantitative research using experimental methodologies because this study necessitates controlling and manipulating one or more independent variables while observing the dependent variable to detect differences based on the independent variables. With a method like this, of course, a tank that is quite efficient can be selected. In terms of profit, it is apparent that it could produce a greater volume of gas than gas to liquid (GTL), because the project of LNG lifespan was more extensive than GTL's. LNG is thus more comercial than GTL.