Liquid Natural Gas Tanks Research Articles

Optimizing seismic performance: Integrating friction dampers into spherical liquid tanks

This study addresses the vital challenge of ensuring the safe storage of Liquid Natural Gas (LNG) in spherical tanks during seismic events, focusing on the crucial balance between meeting seis- mic performance criteria and mitigating economic losses due to potential operational disrup- tions from necessary retrofitting efforts. In response to this challenge, we present a case study on retrofitting an LNG tank near the North Anatolian Fault (NAF) line of Türkiye. Through a com- prehensive seismic evaluation, this study reveals inadequacies in the existing case's compliance with seismic criteria. It suggests a remedy involving the increased stiffness of lateral force-resist- ing members coupled with the utilization of friction dampers. Following the proposed stiffness increase achieved through retrofitting, our approach is fundamental to exploring alternative damping mechanisms designed to enhance the steel column-brace support structure. One of the key design challenges is the unique dynamic behavior of LNG, especially its sloshing during earthquakes, which necessitates a comprehensive understanding of fluid-structure interaction for accurate modeling and analysis. Through a series of transient analyses incorporating actions, we evaluate the effectiveness of the proposed retrofitting measures on the structure. Our findings introduce a feasible and efficient retrofitting strategy, marked by minimal operational interrup- tion, primarily by avoiding the extensive demolition and reconstruction typically required.

Seismic protection of LNG tanks with reliability based optimally designed combined rubber isolator and friction damper

Different types of gas reservoir such as Liquid Natural Gas (LNG) are among the strategic infrastructures, and have great importance for any government or their private owners. To keep the tank and its contents safe during earthquakes especially if the contents are of hazardous or flammable materials; using seismic protection systems such as base isolator can be considered as an effective solution. However, the major deficiency of this system can be the large deformation in the isolation level which may lead to the failure of bearing system. In this paper, as a solution, the efficacy of an optimally designed combined vibration control system, the combined laminated rubber isolator and rotational friction damper, is investigated to evaluate the enhancement of an existing metal tank response under both far- and near-field earthquakes. Responses like impulsive and convective accelerations, base shear, and sloshing height are studied herein. The probabilistic framework is used to consider the uncertainties in the structural modeling, as well as record-to-record variability. Due to the high calculation cost of probabilistic methods, a simplified structural model is used. By using theMont-Carlo simulation approach, it is revealed that this combined isolation system is a highly reliable system which provides considerable enhancement in the performance of reservoir, not only leads to the reduction of probability of catastrophic failure of the tank but also decrease the reservoir damage during the earthquake.Moreover, the relative displacement of the isolation level is controlled very well by this combined system.

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.

An efficient pulse tube cryocooler for boil-off gas reliquefaction in liquid natural gas tanks

Small liquid natural gas (LNG) distribution stations require compact, highly efficient cryocoolers to reliquefy boil-off gas in the LNG tank. This paper describes a pulse tube cryocooler measuring 420mm×690mm×780mm and weighing 180kg. With low input electric power, the relative Carnot efficiency exceeded 20%. Increasing the power to 10kW, the cryocooler produced approximately 1.2kW of cooling at 120K. Approximately 295 normal cubic meters of boil-off natural gas per day can be condensed. If heat transfer in the main heat exchanger is improved, cooling power and efficiency could be further improved. This development offers an efficient, compact, and reliable configuration for energy saving in LNG distribution stations.

Assessment of the seismic effect of insulation on extra-large cryogenic liquid natural gas storage tanks

Insulation is typically used in extra-large double-walled cryogenic storage tanks that are used to store liquid natural gas (LNG). These vessels have been designed with the assumption that the insulation offers negligible structural resistance that might cause structural damage. Observation of the deformation of the insulation in such tanks leads to concern that the insulation may become sufficiently compacted to cause significant load transfer between the inner and outer tank. The inner tank, though protected from most external events by the outer tank, is only designed to contain the liquid gas. It is therefore much more sensitive to seismic effects. In this investigation, simplified and 3D finite element models are used to simulate the interaction effects of the fluid, inner tank, insulation and outer tank. This paper presents an initial analysis of the potential effects of LNG tank insulation under earthquake conditions and assesses the potential for structural damage by comparison of models that do or do not consider the insulation layer. The data reported and statistically sorted include the overturning moment, the base shear, the tank wall stress, and the wave height in the tank. The results show that the insulation layer has certain influence on seismic design of LNG tanks.

An Efficient Pulse Tube Cryocooler for BOG Recondensation in LNG Tanks

Small liquid natural gas (LNG) distribution stations require compact, highly efficient cryocoolers to condense boil-off gas in the LNG tank. This paper reports a pulse tube cryocooler measuring 420*690*780mm and weighing 180kg. Using low input electric power, the relative Carnot efficiency was greater than 20%. Increasing the power to 11kW, the cryocooler produced approximately 1.2kW of cooling at 120K. Approximately 293 normal cubic meters of boil-off NG per day can be condensed. If heat transfer in the main heat exchanger was improved, cooling power and efficiency could be improved. It presents a new efficient, compact and reliable configuration for the energy saving in LNG distribution stations.

Reducing the Economic Risk of LNG Tank Construction under Conditions of Fluctuating Resource Prices

Fluctuating resource prices affect the costs of the materials used in the construction of LNG (liquid natural gas) tanks. In this paper, methods based on the field experience of the writers for the reduction of the cost of LNG tanks in general and in-ground LNG tanks in particular are discussed. Of the various components of the construction cost, the price of steel materials is a significant contributor. Using a newly defined cost impact index, the costs of construction of different types of LNG tanks are compared. Further, by considering actual examples of the construction of in-ground tanks, important issues relating to the use of steel materials are identified and, by using a cost reduction index, recommendations are made for the reduction of the cost risk during fluctuations in resource prices.

Concrete gravity-based structures used for offshore LNG storage and regasification in the Adriatic Sea

A concrete gravity-based structure, used as an offshore liquid natural gas (LNG) receiving and regasification terminal, has been built and installed in the Adriatic Sea. The design, construction and interfaces of the concrete structure posed many challenges which drew on expertise learnt elsewhere in the world of offshore marine concrete structures. The integration of the LNG tanks and the regasification topsides into a compact concrete structure tested the ability to produce a consistent and easily constructed solution. The resulting structure was simple, efficient, robust, durable and the first of its kind.

Boil off gas (BOG) management in Spanish liquid natural gas (LNG) terminals

Spain is a country with six LNG terminals in operation and three more scheduled for 2011. At the same time an increasing number of LNG tanks are under construction to compensate the Spanish lack of underground storage. A method for evaluating the daily boil off generated is presented in this paper. This method is applied to evaluate the increase of BOG to be handle by LNG terminals in 2016, studying the best commercially available solution to be installed. Finally, as a solution to tackle with the BOG a cogeneration plant is suggested. This option will reduce terminal’s operational costs increasing its availability.

Development of a liquid natural gas pump and its application to direct injection liquid natural gas engines

Direct injection gas engines operated with liquid natural gas (LNG) look promising because the energy density-volume ratio of LNG is three times higher than that of compressed natural gas (CNG) and pressurization of LNG to injection pressures is much easier and expends less energy. Based on these considerations, a prototype of an LNG high-pressure pump, which can achieve a pressure as high as 20 MPa, was developed and tested using nitrogen instead of LNG. It was confirmed that the energy consumption of the LNG pump to pressurize an amount of natural gas is one-eighth the energy consumption of the corresponding CNG pump. A direct injection natural gas engine having a 108 mm bore and a compression ratio of 12 was developed for the evaluation of its performance and emissions. The result of the engine experiment made it clear that the indicated thermal efficiency of the gas engine is approximately 44 per cent over a medium and high load range, which is equivalent to that of the corresponding diesel engine. Since the energy required for pressurizing LNG to 15 MPa is 2–3 per cent of the indicated power of the engine, the LNG engine proposed is considered to have the same level of brake thermal efficiency as the corresponding diesel engine. If a truck vehicle is powered by the direct injection LNG engine and carries an LNG tank with a capacity 1.5 times larger than that of gas oil, the cruising distance of the vehicle could be the same as that of a diesel truck.

Rollover in volcanic crater lakes: a possible cause for Lake Nyos type disasters

Seemingly stably stratified fluids, that is a heavier layer of fluid underlying an upper layer of lighter fluid, can overturn if there is a heat flux through the system. Such events are termed “rollover” in the engineering literature (occurring for instance in liquid natural gas tanks). They take place as well in lakes and ponds. In all such cases, the stratification starts off with the heavier, more dense fluid underlying lighter. Convection driven mixing at the stratification interface (due to the heat flux) as well as other processes serves to minimize with time the stabilizing density differences, which may eventually cause the stratification to invert. If gas has been contained under pressure in the lower layer, this gas may explosively vent from the fluid as it suddenly rises to the top such as occurs in liquid natural gas tanks where rollover is a hazard. These processes are quantifiable and are applied here to various scenarios that might refer to volcanic crater lakes whose lower layers are charged with volatiles. Provided herein are some examples of calculated conditions and calculated time of evolution leading to rollover with attendant release of gases from supersaturated ascending fluids. These calculations suggest rollover could occur in volcanic lakes. The August 1986 gas release at Lake Nyos is employed as an example. These estimates were made taking note that water is commonly supersaturated in CO2

Extending a Gas Pipeline Network

This paper describes the use of a mixed-integer programming model for the problem of determining methods of reinforcing and increasing a natural gas pipeline network. The model considers the options of (i) reinforcing pipes, (ii) building new pipes into the network, (iii) setting up of liquid natural gas tanks at certain points on the network, and attempts to find the best policy for satisfying demand levels. Because of the difficulties of solving the resultant mixed-integer problem, the model can only be used for small networks.