Natural Gas Tank Research Articles

Seismic Fragility Analysis of Base-Isolated LNG Storage Tank for Selecting Optimum Friction Material of Friction Pendulum System

The objective of this study is to establish a system for selecting the optimum friction material to meet the seismic performance requirements of a liquefied natural gas tank with a friction pendulum system (FPS). A methodology for determining the optimum frictional material using seismic fragility analysis is suggested, and it is applied to materials with various frictional coefficients for FPS. Seismic fragility curves with two different limit states are developed to determine the optimum friction material, and a methodology for combining fragility curves is proposed. The analysis shows that a lower friction coefficient for FPSs is more appropriate for preventing failure in FPSs and the superstructure investigated in this study.

Effect of cycling and thermal control on the storage and dynamics of a 40-L monolithic adsorbed natural gas tank

Adsorbed natural gas systems have been proposed as a cost-effective storage alternative to compressed and liquefied natural gas. This has led many groups to search and design sorbent materials with large methane storage capacities since natural gas is approximately 90% methane. The other 10% of natural gas contains larger hydrocarbons which can decrease the useable storage capacity of adsorbent systems. In this work, the effect of large hydrocarbons on the storage and dynamics of a 40-L adsorbed natural gas system, containing 20.5 kg of monolithic carbon adsorbent, produced by the University of Missouri, is reported. It was found that over the course of 20 cycles, due to the retention of 1.9 kg of non-methane components by the monoliths, the useable volumetric storage dropped 16%, and the amount of gas delivered dropped 10%. A second cycling experiment found that by using thermal control while the system discharged, the mass retention decreased to 0.91 kg, and the useable volumetric storage and delivered mass only dropped 7% and 5%, respectively. The effects of the mass retention, storage loss, and thermal control on the system’s charge and discharge dynamics were then analyzed to provide a complete picture of the long-term effects of cycling large scale adsorbed natural gas systems with and without active thermal control.

Field application of freezing technology for social infrastructures

There are numerous methods to prevent seepage flow and ground improvement methodologies such as cement grouting, sheet piling, and the membrane method. In this paper, we present case histories of freezing technology applications in the construction of a deep tunnel sewerage system, undersea highway tunnel, and liquefied natural gas tank. Heaving pressure measurements for various soil types around a liquefied natural tank are compared with existing data. In this paper, we present temperature variations at the bottom and side of a liquefied natural gas tank. Our findings show that ground-freezing technology is very effective in controlling ground water infiltration into underground structures as well providing soil reinforcement in the soft ground.

Effect of indoor air quality on the natural history of asthma in an urban population in Poland.

Background: Indoor air pollution may have an impact on asthma. Objective: To evaluate the influence of indoor air pollution on the natural history of asthma. Methods: Data collection by using the European Community Respiratory Health Survey and International Study of Asthma and Allergies in Childhood standardized questionnaire (N = 18,617) and medical examinations (N = 4783) in selected Polish regions was used. Statistical analysis was performed by using the χ² test. A value of p < 0.05 was considered statistically significant. Results: Questionnaire results demonstrated that people who used the central heating system were less likely to declare the occurrence of asthma (odds ratio [OR] 0.84) and were corroborated with clinical findings of moderate asthma (OR 0.35). Symptomatic asthma occurred more frequently in people who used a solid-fuel heating device (OR 1.36) and electric heaters (OR 1.54). The use of cooking appliances with municipal natural gas (OR 1.77) and gas storage tanks (OR 2.03) was correlated with more frequent declarations of asthma. Symptomatic asthma was more common among people who smoked for at least 1 year (OR 2.26) and those who smoked over the course of the preceding month (OR 1.60). Passive exposure to tobacco smoke provided for a 1.5-fold increase in the incidence of symptomatic asthma (OR 1.53), regardless of the time of exposure. Conclusion: Both active and passive tobacco smoke exposure as well as the use of certain types of heating and cooking appliances have a significant impact on the incidence of asthma and the intensification of its symptoms in rooms with limited air exchange. Highlights of the study included the following: (1) central heating had an amelioratory effect on asthma, (2) heating technologies used at home had a significant impact on the incidence of asthma, and (3) devices used for cooking (municipal and cylinder gas stoves) played an important role in the intensification of asthma symptoms.

Weldpool shape investigation in fiber laser welding of Cr-Ni-Mn-N austenitic steel

Austenitic stainless steels are the main material for liquid natural gas tanks. Traditional Cr-Ni steels can be replaced by cheaper C-Ni-Mn-N ones, but there are difficulties with the implementation of welding for such materials, including nitrogen loses and hot cracking. Fiber laser welding can be applied to partially solve these problems, however the process optimization is needed to provide the optimal weldpool shape. In this work it was shown that the increasing of the laser beam power leads to the appearance of the second plasma torch and the area of open surface of the weldpool on the back side increases significantly, that can influence the interaction between the melted steel and the environment.

Topology optimisation of biphasic adsorbent beds for gas storage

Adsorption is a retention mechanism of fluid molecules on solid surfaces and presents a wide range of applications, such as fuel storage, refrigeration and separation processes. This work describes the modelling of gas adsorption on porous media and presents an optimisation approach for the design of adsorption systems based on biphasic adsorbent beds by topology optimisation. A comprehensive formulation for the adsorption phenomenon is presented, detailing the derivation of governing equations and respective weak forms and discretisation for the implementation of the finite element method (FEM). A new topology optimisation material model based on offset hyperbolic tangents is introduced. The derivation of sensitivities is presented in detail, based on a transient adjoint problem. A diverse set of optimised adsorbed natural gas (ANG) tanks, considering real material properties of activated carbon and steel, is presented. Results indicate the suitability of the method in optimising the distribution of phases across adsorbent beds and show that biphasic ANG tanks can perform significantly better than traditional tanks.

Evaluating methane adsorbed film densities on activated carbon in dynamic systems

Abstract Dynamic methane loading and discharge experiments on a 40 L adsorbed natural gas tank containing 20.5 kg of monolithic carbon adsorbent have been combined with pore volume data from subcritical nitrogen isotherms to evaluate the density and dynamic properties associated with adsorbed methane. The time-dependent density of the adsorbed gas was evaluated for narrow and wide micropores. The temperature-dependent adsorbed film volume was determined from the Ono-Kondo model and compared with the total micropore volume. The resulting adsorbed methane density evolves in two distinct parts. The density increases rapidly during the beginning of the loading process and increases slowly after narrow pores reach saturation. The narrow pores’ saturated adsorbed gas densities ranged from 0.26 – 0.35 kg/L, depending on the choice of film volume. The density of wide micropores was found to be highly dependent on the loading procedure due to the expected temperature dependence of the film volume. During discharge, it was found that the wide micropores deplete early while narrow micropores deplete slowly which causes the less than 100% efficient discharges seen in adsorbed natural gas systems. These density models have been applied to accurately predict the gravimetric excess adsorption of other carbon adsorbents at 35 bar and explain previously published pressure and temperature relations during tank loading.

The process of liquefied natural gas

In this paper, the analysis of liquefied natural gas process plant technology, into the device before the natural gas compression, and then through the MEA aqueous solution to remove CO2. Finally, the compressed water removed; clean natural gas before entering the liquefaction unit. In the liquefaction unit, the high-pressure natural gas is cooled and liquefied deep. The required cooling capacity is obtained by circulating the gas turbine to drive the closed mixed refrigerant nitrogen, methane, ethylene, propane and other components, and liquefied natural gas (LNG), which is finally stored in an atmospheric tank through a liquefied natural gas container or liquefied natural gas tanker for distribution. The recycle of the recycle refrigerant is carried out by means of environmental conditions. The heating medium required during the installation process is the hot oil heated by the exhaust gas of the gas turbine. The liquefied gas in the liquefied natural gas tank is compressed to regenerate the desiccant and then sent to the gas turbine as the fuel gas.

Controlled charge and discharge of a 40-L monolithic adsorbed natural gas tank

The University of Missouri constructed a prototype adsorbed natural gas tank for low-pressure storage of methane on natural gas vehicles. The tank contains monolithic nanoporous carbon with storage capacities up to 0.11 kg methane/L carbon and 0.19 kg methane/kg carbon at 35 bar and 25 °C which is 4.5 times larger than a tank without any adsorption would store at 35 bar. In this paper, we report the performance characteristics of the tank under different charge and discharge protocols. The tank was found to be able to be reach 80% of its full capacity in 3 min with total filling times being better or comparable to electric vehicles. The ability to use different filling procedures to counteract the storage loss due to the 65+ °C temperature rise is also explored. Pressure control during discharges, using a proposed fuel extraction system, is also explored which resulted in doubling a car’s highway drivetime and discharge efficiencies of 90%. The temperature and storage evolution is also analyzed to give new insights on the dynamics of monolithic carbon systems which have not been extensively studied in the literature. The results support that adsorbed natural gas systems combined with an effective compressor, possibly also with switching from a cold tank module to a warm module, can become a viable alternative to compressed or liquefied natural gas.

Stress Analysis of LNG Storage Tank Outlet Pipes and Flanges

The liquefied natural gas (LNG) tank outlet pipe is the weak part of any LNG vaporizing station. Due to the ultralow temperature characteristics of LNG, pipeline damage or leakage may cause major accidents. This paper used the finite element analysis method and the CAESAR II software to analyze the stresses of LNG storage tank outlet pipes and flanges in a LNG vaporizing station, the influencing factors (compensator type, compensator position, LNG density, pressure, temperature) are analyzed, and stress reduction measures are discussed. According to the results of the analysis, the following main conclusions can be obtained: (1) the most dangerous working condition of the LNG storage tank outlet pipe is the precooling condition; under this condition, the comprehensive stress, displacement and support force are the largest; (2) compared with the Z-type and L-type compensators, the effect of the π-type compensator to reduce the stress of the low temperature pipe is the best; (3) when the length of the cold tightening unit is 40% of the cold shrinkage, the stress reduction effect is the best.

Heat transfer modelling of Liquified Natural Gas (LNG) Tanks

Heat transfer modelling of Liquified Natural Gas (LNG) Tanks

Topological Network Inversion Method of Fire Source Location for Liquefied Natural Gas (LNG) Storage

Abstract Liquefied Natural Gas (LNG) tank fire and explosion accident consequences and losses are very serious. Accident inversion method can provide the basis for accident prevention, but there are still some problems on the LNG tank fire with inversion method. Therefore, the topological network model and inversion method of LNG tank fire accident are proposed in this thesis. Firstly, the topology model of LNG tank fire inversion is established, and the optimal estimator of the shortest path is proposed according to the weighted edge topological network structure, so as to determine the fire location. Case study is applied to a LNG tank farm. The results show that the position of the fire source obtained by the proposed method is the same as that of the actual accident, which proves the feasibility of the method and provides a basis for reducing the fire losses and preventing accidents of LNG.

Adsorbed Natural Gas Tank feeded with Liquid Natural Gas

This paper present the idea of a natural gas reservoir, which uses technology of gas storage by adsorption on activated carbon. Such reservoir can be feeded with Liquid Natural Gas. The framework of article includes theoretical principals of gas-solid physical adsorption, and explains most important concepts associated with it. Moreover, concept of such tank and working regime is presented. Selected subject is very promising in the field of natural gas storage, although this is still a niche issue. Lack of universal models of gases physical adsorption made it very difficult to predict the runs of processes occurring in the proposed reservoir, which is why this project was based on models confirmed during in the earlier studies.

Nonlinear sloshing in rectangular tanks under forced excitation

A numerical code is developed based on potential flow theory to investigate nonlinear sloshing in rectangular Liquefied Natural Gas (LNG) tanks under forced excitation. Using this code, internal free-surface elevation and sloshing loads on liquid tanks can be obtained both in time domain and frequency domain. In the mathematical model, acceleration potential is solved in the calculation of pressure on tanks and the artificial damping model is adopted to account for energy dissipation during sloshing. The Boundary Element Method (BEM) is used to solve boundary value problems of both velocity potential and acceleration potential. Numerical calculation results are compared with published results to determine the efficiency and accuracy of the numerical code. Sloshing properties in partially filled rectangular and membrane tank under translational and rotational excitations are investigated. It is found that sloshing under horizontal and rotational excitations share similar properties. The first resonant mode and excitation frequency are the dominant response frequencies. Resonant sloshing will be excited when vertical excitation lies in the instability region. For liquid tank under rotational excitation, sloshing responses including amplitude and phase are sensitive to the location of the center of rotation. Moreover, experimental tests were conducted to analyze viscous effects on sloshing and to validate the feasibility of artificial damping models. The results show that the artificial damping model with modifying wall boundary conditions has better applicability in simulating sloshing under different fill levels and excitations.

Quantifying alkane emissions in the Eagle Ford Shale using boundary layer enhancement

Abstract. The Eagle Ford Shale in southern Texas is home to a booming unconventional oil and gas industry, the climate and air quality impacts of which remain poorly quantified due to uncertain emission estimates. We used the atmospheric enhancement of alkanes from Texas Commission on Environmental Quality volatile organic compound monitors across the shale, in combination with back trajectory and dispersion modeling, to quantify C2–C4 alkane emissions for a region in southern Texas, including the core of the Eagle Ford, for a set of 68 days from July 2013 to December 2015. Emissions were partitioned into raw natural gas and liquid storage tank sources using gas and headspace composition data, respectively, and observed enhancement ratios. We also estimate methane emissions based on typical ethane-to-methane ratios in gaseous emissions. The median emission rate from raw natural gas sources in the shale, calculated as a percentage of the total produced natural gas in the upwind region, was 0.7 % with an interquartile range (IQR) of 0.5–1.3 %, below the US Environmental Protection Agency's (EPA) current estimates. However, storage tanks contributed 17 % of methane emissions, 55 % of ethane, 82 % percent of propane, 90 % of n-butane, and 83 % of isobutane emissions. The inclusion of liquid storage tank emissions results in a median emission rate of 1.0 % (IQR of 0.7–1.6 %) relative to produced natural gas, overlapping the current EPA estimate of roughly 1.6 %. We conclude that emissions from liquid storage tanks are likely a major source for the observed non-methane hydrocarbon enhancements in the Northern Hemisphere.

Toward Safer, Smarter, and Greener Ships: Using Hybrid Marine Power Plants

Electrical power plants with dieselgenerator sets segregated (i.e., the diesel generator sets are divided into different power buses and physical stations on ships and rigs) on several power buses have become the preferred solution for ships with various operational profiles and corresponding power demands. Examples of such ships are dynamically positioned (DP) vessels with electric power plants in the range of 10-80 MW used in the offshore oil and gas industry for service, drilling, intervention, and production operations (Figure 1). The operations are characterized as safety critical and take place year-round, with large variations in the environmental loads acting on the ship, e.g., wind, waves, ocean currents, and sea ice. Electrical power plants have also become the preferred solution for cruise ships, ferries, navy ships, liquefied natural gas tankers, and icebreakers. The electric energy production may be powered by a hybrid marine power plant consisting of diesel or gas engines and integrated energy storage devices (ESDs) such as banks of batteries. Proper design and control systems can deliver significant fuel savings to make the ships greener and safer.

40 years old LNG stainless steel pipeline: Characterization and mechanical behaviour

Stainless steel is a corrosion resistant metal that has now wide record of good performance in several aggressive media, in spite of which is not fully immune to different types of attack. In present work is presented the performance of 304 stainless steel as forming part of the tubes of a tank that has been operating from 1964 for Liquefied Natural Gas storage. The stainless steel tubes are part of a pipeline connecting the Liquefied Natural Gas tanks TK-1200A/B at the Barcelona plant. The pipeline had been continuously operating for more than 40 years, with cooling cycles from ambient temperature down to cryogenic temperatures. The paper shows that the working conditions and the marine environment did not embrittle or modify the properties of the tubes.

Developing a marine engineering centre of excellence for competency-based training

Institutes imparting training in marine engineering require replication of shipboard ambience for strengthening the competencies. For building an engineering centre for training, five options at different physical levels were considered based on a model of a new liquefied natural gas tanker ship build. A mock-up facility, simulator, full-scale engine room, scaled down version and a combination arrangement with live and dummy equipment were the options. Analytic hierarchy process was applied for selecting a suitable option based on criteria of cost, effectiveness in attaining competencies, practicability and environmental conduciveness. Analyses were carried out on the eigenvalues based on eight subselection criteria. The combination of live equipment (boilers and turbo alternator) and non-live shipboard equipment (auxiliaries) was chosen based on the global weightages obtained from the pairwise comparison matrix computations. The reliability was ascertained from the consistency index which was less than 0.1. For selection of the learning modes and the equipment, a constructivist approach of learners reflecting and choosing the learning mode was adopted. Industry practitioners were made into learner groups composed of trainers, shipboard personnel and company personnel. Established competencies were assigned as scores to the different learning modes. ANOVA application and statistical methods were used to analyse the scores to verify if there were too much variation in the choices. The calculated F ratio values were low (0.14 to 0.40) compared to the reference values indicating that the choices were even. The chi-squared test indicated that the group composition did have an influence on choosing the learning mode and equipment for training. The objective of identifying the learning mode and equipment for the training centre was achieved.

Liquefied Natural Gas Tanks for Suppressing Pitching Motions of FLNG Facility

Floating liquefied natural gas (FLNG) facility using partially filled tanks for control of pitch motion response to wave-exciting forces is investigated in this paper. The governing equations for sloshing analysis of rectangular tanks under pitch motion excitation are first established, then the spatial (boundary- value) partial derivatives are approximated by finite differences. The uncoupled pitch equation of FLNG is derived by assuming that pitch is uncoupled from other modes of vibration. By using state-space model to represent fluid-memory effect, the pitch equation can be transformed to first- order ordinary differential equations which can be solved with sloshing equations simultaneously with the given initial conditions. By using the proposed coupling model for FLNG facility and the liquefied natural gas (LNG) tanks, the performance of partially filled tanks for suppressing pitching motions of FLNG facility is numerically assessed. The parametric studies on the example FLNG show that there is a beneficial filling level by which the pitch motion of FLNG can be considerably reduced.

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.