Floating Liquefied Natural Gas Research Articles

Hydrodynamic interaction between FLNG vessel and LNG carrier in side by side configuration

The Floating Liquefied Natural Gas (FLNG) is a new type of floating platform for the exploitation of stranded offshore oil/gas fields. The side by side configuration for the FLNG vessel and the LNG carrier arranged in parallel is one of the possible choices for the LNG offloading. During the offloading operations, the multiple floating bodies would have very complex responses due to their hydrodynamic interactions. In this study, numerical simulations of multiple floating bodies in close proximity in the side by side offloading configuration are carried out with the time domain coupled analysis code SIMO. Hydrodynamic interactions between the floating bodies and the mechanical coupling effects between the floating bodies and their connection systems are included in the coupled analysis model. To clarify the hydrodynamic effects of the two vessels, numerical simulations under the same environmental condition are also conducted without considering the hydrodynamic interactions, for comparison. It is shown that the hydrodynamic interactions play an important role in the low frequency motion responses of the two vessels, but have little effect on the wave frequency motion responses. In addition, the comparison results also show that the hydrodynamic interactions can affect the loads on the connection systems.

Design and Optimization of Natural Gas Liquefaction and Recovery Processes for Offshore Floating Liquefied Natural Gas Plants

A natural gas liquefaction and liquid recovery sequence is proposed for top-side offshore floating liquefied natural gas processing. During liquefaction, a single mixed refrigerant is separated into heavy and light key components, separately compressed after the main cryogenic heat exchanger and then mixed again to make a single mixed refrigerant. The proposed liquefaction cycle has a simple, compact structure and is suitable for power-efficient, offshore, floating liquefied natural gas liquefaction. The natural gas liquid recovery process employs space- and energy-efficient dividing wall columns for the integration of depropanization and debutanization. The columns were optimized by response surface methodology. A compact top dividing wall column configuration could reduce total annual costs. A combined process integrating natural gas liquefaction and liquid recovery is finally proposed.

Investigation on the hydrodynamic performance of an ultra deep turret-moored FLNG system

Hydrodynamic performance of an ultra deep turret-moored Floating Liquefied Natural Gas (FLNG) system is investigated. Hydrodynamic modeling of a turret-moored FLNG system, in consideration of the coupling effects of the vessel and its mooring lines, has been addressed in details. Based on the boundary element method, a 3-D panel model of the FLNG vessel and the related free water surface model are established, and the first-order and second-order mean-drift wave loads and other hydrodynamic coefficients are calculated. A systematic model test program consisting of the white noise wave test, offset test and irregular wave test combined with current and wind, etc. is performed to verify the numerical model. Owing to the depth limit of the water basin, the model test is carried out for the hydrodynamics of the FLNG coupled with only the truncated mooring system. The numerical simulation model features well the hydrodynamic performance of the FLNG system obtained from the model tests. The hydrodynamic characteristics presented in both the numerical simulations and the physical model tests would serve as the guidance for the ongoing project of FLNG system.

Experimental investigation of effects of inner-tank sloshing on hydrodynamics of an flng system

The present research focuses on experimentally clarifying the effect of inner-tank sloshing on the hydrodynamics of an Floating Liquefied Natural Gas (FLNG) system. Through the comparisons of the results obtained from the model tests carried out with the vessel model ballasted with liquid and solid cargo separately, the effects of the inner-tank sloshing on the hydrodynamics of an FLNG system are highlighted and presented. Statistical languages of the maximum, minimum, mean values and the standard deviations and power density spectra calculated with the help of the algorithm of Fast Fourier Transformation (FFT) are provided. It is concluded that the effects of the inner-tank sloshing on the responses of the FLNG system are sensitive to wave excitation frequencies, and that the effects of the inner-tank sloshing play an important role, particularly in the roll motion of the FLNG hull. The outcome of the proposed technique would offer constructive feedback, which can lead to more practical applications and can serve as a reference for the verification of the potential numerical simulations by other researchers.

Operability of a floating LNG production facility

The advantages of offshore floating liquefied natural gas (FLNG) production include reduced environmental footprints and potential reduced costs for remote and marginal field development. Moving a conventional land-based LNG plant offshore, however, does not come without its fair share of challenges. Ensuring operability—and hence availability—is one of those challenges. While offshore natural gas process technology selection is largely dictated by limited deck space and high safety focus, a crucial aspect in the design and operation of any of the equipment onboard an FLNG facility is the motion characteristics of the hull in the metocean environment. In fact, hull motions affect the performance of the LNG storage tanks, cargo offloading systems, module structural connections, and nearly every single piece of topsides equipment. Determining the required performance of the hull, however, involves an iterative process between the design of topsides equipment and the configuration of the hull. On one hand, the hull is optimised to minimise its responses to the operating environment and to best suit any operational limitations of process systems and equipment. On the other hand, the process systems and equipment are modified to perform under greater hull motions. The cryogenic transfer of LNG between an offshore floating production facility and its designated LNG carriers is one of the weakest links in the total chain of offshore floating LNG development. It involves two floating systems, working in close proximity, in the dynamic offshore environment. The operability of this greatly affects the availability for LNG offloading and overall delivery. The purpose of this paper is to review the operability aspects of an FLNG project, particularly those affected by hull motions. State-of-the-art operability design and assessment methods will be discussed, including outcomes of some of the dedicated research and development programs that have made FLNG a foreseeable reality for Australian and worldwide offshore natural gas projects and prospects.

Numerical investigation on the hydrodynamic difference between internal and external turret-moored FLNG

Motion responses of the floating liquefied natural gas (FLNG) hull and the mooring loads in a 100-year return environmental condition are predicted with the help of the well known coupled dynamic analysis code DeepC. A ship-shaped turret-moored FLNG moored by 4×3 chain-polyester-chain lines in 1.5 km depth of water is studied. Two types of turrets such as internal and external turrets, resulting from different locations of the turrets, are adopted respectively in the numerical simulations. Motion responses of the FLNG hull and forces of the mooring lines obtained from the internal turret case and external turret case are compared with each other. Significant differences are obtained. Statistic analysis is also used to analyze the comparison results, and effects of the turret location on the FLNG hydrodynamic characteristics are summed up. The conclusion regarding the hydrodynamic differences between internal and external turret-moored FLNG systems would provide help for design of the FLNG system.

Investigation of a Floating-Liquefied-Natural-Gas Unit for Brazilian Waters

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 20677, ’Evaluation of a Floating Liquefied Natural Gas for Brazilian Scenarios,’ by A.P.F. Teles, A.S. de Abreu, A.C. Saad, D.C. deMello, F.B. Campos, J.P. Silva, L.F.N. Quintanilha, and M.D.A.S. Ferreira, Petrobras R&D Center, originally prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed. The latest discoveries of oil and gas in the Brazilian offshore area present new challenges for gas transportation because of their distance from the coast. For these new scenarios, floating-liquefied-natural-gas (FLNG) units may be a good solution for the natural gas volume produced. Because this technology has not been proved yet, there are many challenges to overcome to turn FLNG into an economically and technically feasible solution. Introduction The international natural-gas market has been growing at a very high rate in the last decade. The mature technologies for natural-gas bulk transportation are pipelines and liquefied natural gas (LNG) considering a supply chain based on onshore liquefaction plants and LNG carriers. The latest discoveries of oil and gas in the Brazilian offshore area present new challenges for gas transportation because of their distance from the coast. Offshore pipelines are economically feasible for short or medium distances, depending on water depth. The concept of an FLNG combines a tailor-made vessel with isolated cryogenic tanks in the hull, a liquefaction plant on the topside, and offloading systems on the deck. Because the FLNG concept combines existing and proven onshore and offshore technologies, integration is a critical issue. Development Issues LNG. LNG is obtained when a stream of suitably treated natural gas is cooled to −160°C, at atmospheric pressure. The gas-to-liquid phase change reduces the gas volume 600 times. LNG is the chosen technology for sea transportation in carriers of large quantities of natural gas to distant markets when a pipeline is not feasible. The LNG sea-transportation model has, basically, four items: the field processing plant, the baseload liquefaction plant, the carriers, and the regasification terminal. The field processing plant receives the reservoir production, does the primary separation, and treats the gas to avoid hydrate formation in and corrosion of the exporting pipeline. The baseload liquefaction plant further treats the gas to remove heavy hydrocarbons and impurities, adjusting the natural-gas composition to the process requirements and to the LNG sales specifications. This plant usually is placed near a marine terminal where special carriers, with isolated cryogenic tanks, are filled with LNG. These carriers transport the LNG to the regasification terminal commonly placed near a marine terminal. Liquefaction Technology The baseload LNG industry has more than 40 years experience, with the first plants consisting of simple liquefaction technologies based either on cascade or mixed-refrigerant (MR) processes with train capacity less than 1 million tons per year.

What’s Different about Floating LNG? A Legal and Commercial Perspective

Liquefied natural gas (LNG) is of clear strategic importance to many countries. Floating LNG (FLNG) represents an opportunity, in the case of liquefaction, to develop marginal gas fields and, generally, to match supply and demand as never before. However, the advent of FLNG project developments will inevitably bring with it a unique set of technical, commercial and regulatory challenges. Lawyers will have a large part to play in ensuring that these challenges are adequately addressed, assisting project sponsors in securing the requisite permits and approvals under existing applicable national and international regulatory frameworks or helping to negotiate appropriate regulatory frameworks in jurisdictions where the existing framework does not cater for the peculiarities of FLNG. This article surveys some key legal and commercial issues in the structuring of the FLNG projects by comparison with onshore LNG projects and includes a case study on Indonesia.