Offshore LNG Research Articles

The impact of LNG offshore terminal on sea temperature and sea currents in the northern Adriatic Sea

The aim of this paper is to simulate the impact of a potential offshore LNG terminal on sea temperature (in autumn and spring/ summer) and sea currents (in autumn/winter) at three different depths (at the sea surface, at 25 m depth and at the seabed) in the northern Adriatic Sea from 14 November 2015 to 06 August 2016 using the Regional Ocean Modelling System (ROMS) model. The location of the potential offshore LNG terminal Istria (in the northern Adriatic Sea) was selected using the visual PROMETHEE method. The potential LNG terminal uses seawater for LNG heating and the seawater cooled to a temperature of 9°C returns to the marine environment. Although the differences in sea temperature with and without the discharge fit within normal temperature ranges, the simulations show that the discharge changed the speed and direction of sea currents at the sea surface not only in the wider northern Adriatic, but in the entire Adriatic. This is probably due to the specific circulation in the Adriatic, where cold water affects the geostrophic balance, an important part of the circulation field that depends on density (a function of salinity and temperature). Atmospheric conditions in the broader vicinity of the LNG terminal would also be affected by redistribution of air-sea fluxes due to changes in surface temperature. Changes in circulation would alter environmental conditions by redistributing nutrients, oxygen, etc. Further multi-year simulations of changes in the circulation system are needed, but other physical parameters (density, salinity, river inflow...) should also be included in the simulations to determine the cumulative impact of a potential LNG terminal on the marine environment.

Comparative study of three insulation materials installed on type C independent tank for offshore LNG transportation

The traditional choice of insulation material for offshore LNG transportation with type C independent tank was polyurethane foam (PUF). However, aiming to further cut down the insulation cost and spare additional arrangement space, the requirement of searching for the alternative materials still exists. Polyisocyanurate board (PIRB) and silica aerogel blanket (SAB) are chosen as candidates in this study since these two materials have been proved to be available in other fields. Despites their advantages, the seams and joints due to the specific installation techniques for PIRB and SAB could be the causes of potential defects when transporting cryogenic liquid. In this paper, the comparative study of three materials associated with their specific installation techniques was conducted to discuss if PIRB and SAB are available for offshore LNG transportation. Therein, the insulation performances were investigated through the evaporation experiment of LN2 with a 1.5 m3 type C experimental tank. The equivalent conductive model was adopted in the numerical analysis with finite element method (FEM) to determine the temperature field of insulation and the absorbed heat from the LN2 evaporation. It is proved that three types of insulation materials are well behaved and available for transporting cryogenic liquid. In respect of the thermal resistance, the ranking of three types of insulation materials is: SAB, SPF and PIRB. Higher thermal resistance of insulation leads to thinner thickness and additional arrangement space in the cargo hold, and more ship construction cost can be cut down due to the possible scaling down of ship dimensions. However, from the perspective of insulation material cost, the cost reduction due to the insulation thickness decrease is not significant as the tank continually scales up, and it is more practical to apply SPF or PIRB on a full-scale type C independent tank.

Fracture Toughness Characteristics of High-Manganese Austenitic Steel Plate for Application in a Liquefied Natural Gas Carrier

High-manganese austenitic steel was developed to improve the fracture toughness and safety of steel under cryogenic temperatures, and its austenite structure was formed by increasing the Mn content. The developed high-manganese austenitic steel was alloyed with austenite-stabilizing elements (e.g., C, Mn, and Ni) to increase cryogenic toughness. It was demonstrated that 30 mm thickness high-manganese austenitic steel, as well as joints welded with this steel, had a sufficiently higher fracture toughness than the required toughness values evaluated under the postulated stress conditions. High-manganese austenitic steel can be applied to large offshore and onshore LNG storage and fuel tanks located in areas experiencing cryogenic conditions. Generally, fracture toughness decreases at lower temperatures; therefore, cryogenic steel requires high fracture toughness to prevent unstable fractures. Brittle fracture initiation and arrest tests were performed using 30 mm thickness high-manganese austenitic steel and SAW joints. The ductile fracture resistance of the weld joints (weld metal, fusion line, fusion line + 2 mm) was investigated using the R-curve because a crack in the weld joint tends to deviate into the weld metal in the case of undermatched joints. The developed high-manganese austenitic steel showed little possibility of brittle fracture and a remarkably unstable ductile fracture toughness.

Analysis of offshore LNG storage and transportation technologies based on patent informatics

As International Maritime Organization (IMO) 2020 Regulations on sulphur limits took effects, increasing interests in LNG are witnessed worldwide, since LNG is believed to be a promising alternative for the reduction of air pollution. The aim of this paper is to study the technological advancements of offshore LNG storage and transportation technologies based on patent informatics. Patent informatics is the analysis of patents in order to unveil patent information. In this work, past patenting activities in the studied technological domain were reviewed, the most active technological participants were identified, worldwide patent portfolios were constructed, and text mining and clustering of the key technologies were conducted. Results of the study can help to identify technological opportunities in the area of offshore LNG storage and transportation, and may serve as a reference for decision makers to formulate strategic plan for future technological development.

Technology Focus: Natural Gas Processing and Handling (April 2021)

In 2020, the spot prices of natural gas hit a record low in the US, reaching the lowest annual average price in more than a decade. Based on US Energy Information Administration (EIA) data, the average annual spot price reported in 2020 was $2.05 per million British thermal units (MMBtu). In the first few months of the year, reports from the EIA showed that natural gas prices started declining amid mild winter temperatures that resulted in a decline in the demand for natural gas for space heating. In March 2020, following the onset of the COVID-19 pandemic, the already declining natural gas prices plummeted further. This decline continued through the first half of the year. The EIA reported the average monthly Henry Hub spot price in the first 6 months at $1.81/MMBtu. June saw the lowest monthly natural gas price in decades (Henry Hub price aver-aged $1.66/MMBtu). Natural gas prices recovered in the second half of the year as natural gas production decreased and global exports of liquefied natural gas increased. Natural gas consumption in the residential, commercial, and industrial sectors declined in 2020, according to the EIA. Milder winter temperatures were a major contributor in the first quarter of the year, but overall declining consumption was attributed to reduced economic activities as a result of the COVID-19 pandemic. On the other hand, the consumption of natural gas for electric power generation registered an overall increase of 2% more than the 2019 average. According to the EIA, citing S&P Global Platts, this increase was attributed to power producers switching to cheaper natural gas from coal to meet the increased demand for electric power for cooling as summer temperatures increased. The EIA in its Annual Energy Outlook 2021 projects that the industrial and electric power sectors and net exports will drive the growth in US energy consumption between 2020 and 2050. Natural gas consumption in other sectors is expected to increase steadily or remain flat. The EIA forecasts that natural gas production will increase as consumption increases and prices will stay low relative to past prices. The EIA expects continued growth in natural gas exports as natural gas production surpasses natural gas consumption. Globally, the International Energy Agency forecasts a recovery in global demand for natural gas in 2021 led by growth in the Asia Pacific region as emerging markets recover. The US will continue to play a significant role as one of the largest producers and contributors to natural gas supply growth. Recommended additional reading at OnePetro: www.onepetro.org. SPE 200300 - Overcoming Challenges in the Development of Underground Gas Storage by Ammar Alali, Saudi Aramco, et al. OTC 30602 - Offshore LNG and Gas Monetization by Femi Adeoye Alabi, Total SPE 200147 - Development of the Underground Gas Storage and Construction of the Salt Cavern Storage in China by Peng Chen, CNPC, et al.

Multicriteria decision support to evaluate potential long-term natural gas supply alternatives: The case of Greece

This paper assesses 27 alternative natural gas supply corridors for the case of Greece, according to a multicriteria analysis approach based on three main pillars: (1) economics of supply, (2) security of supply, and (3) cooperation between countries. The alternatives include onshore and offshore pipeline corridors and LNG shipping, determined after exhaustive investigation of all possible existing and future routes, taking into consideration all possible natural gas infrastructure development projects around Greece. A multicriteria additive value system is assessed via the robust ordinal regression methodology, aiming to support the national energy policy makers to devise favorable strategies, concerning both long-term national natural gas supplies and infrastructure developments. The obtained ranking shows that noticeable alternative corridors for gas passage to Greece do exist both in terms of maritime transport of LNG and in terms of potential future pipeline infrastructure projects.

연강(Mild Steel)의 극저온 파괴 거동에 대한 실험적 연구

LNG선이나 해양플랜트 같은 설비나 구조물은 작동 조건을 고려할 때, 특히 부재마다 가지는 고유한 연성 취성천이온도(Ductile to Brittle Transition Temperature, DBTT)를 고려하여 설계되어야 한다. 본 연구에서는 해양플랜트 및 LNG선에 hull plate로 쓰이는 A-grade 연강(mild steel)에 대해 DBTT를 샤르피 V-노치(CVN) 실험을 통해 알아보았고 파괴형상을 통한 파괴거동을 살펴보았다. 그 결과 온도가 감소함에 따라 충격 흡수에너지는 감소함을 보였다. Upper shelf energy region과 lower shelf energy region이 나타나고 그 사이 구간의 천이점을 통해 DBTT가 결정되었다. 파괴형상에서는 upper shelf energy region에서 수많은 딤플이 연성파괴 형상으로 관찰되고 lower shelf energy region에서는 전형적인 취성파단형상이 관찰되었다. 이를 통해 BCC 구조를 가지는 A-grade 연강은 upper shelf energy 구역과 lower shelf energy구역을 보이고 그 사이 구간의 천이점에서 급격하게 온도가 떨어지는 DBTT구간을 뚜렷하게 보이는 특성을 알 수 있었다. Considering for plants and structure under extreme conditions is required for the successful design, especially temperature and pressure. The ductile-brittle transition temperature (DBTT) for the materials under extreme condition needs to be considered. In this study, A-grade mild steel for the LNG carrier and offshore plant was examined by performing low-temperature Charpy V-notch (CVN) impact tests to investigate DBTT and the fracture toughness. The absorbed energy decreased gradually with the experimental temperature, which showed an upper-shelf energy region, lower shelf energy region, and transition temperature indicating DBTT. In addition, the fracture surface morphologies of the mild steels indicated ductile fractures at the upper-shelf energy level, with wide and large-sized dimples, whereas a brittle fracture surface, where was observed at the lower-shelf energy level, with both large and small cleavage facets. Based on the experimental results, ductile brittle transition temperature was estimated in about <TEX>$-60^{\circ}C$</TEX>.

Toward a Probabilistic Approach to Determine Nominal Values of Tank Sloshing Loads in Structural Design of Liquefied Natural Gas FPSOs

The aim of this study is to develop a new probabilistic approach to determine nominal values for tank sloshing loads in structural design of LNG FPSO (liquefied natural gas, floating production, storage, and offloading units). Details of the proposed procedure are presented in a flow chart showing the key subtasks. The applicability of the method is demonstrated using an example of a hypothetical LNG FPSO operating in a natural gas site off a hypothetical oceanic region. It is noted that the proposed method is still under development for determining reliable estimates of extreme sloshing induced impact loads. It is concluded that the developed method is useful for determining the sloshing design loads in ship-shaped offshore LNG installations in combination with virtual metocean data and operational conditions.

Side-rectifier divided wall column for offshore LNG plant

A side-rectifier DWC (divided wall column) is proposed to replace the whole FLNG (floating liquefied natural gas) plant, which comprises of three distillation columns in the conventional system. The proposed column is compact equipment suitable to harsh offshore operation of the gas plant, which is operated at low pressure to reduce the investment and electricity costs. The economics, thermodynamic efficiency and operational difficulty of the side-rectifier DWC are evaluated and compared with the conventional system. The heating and cooling duties of the side-rectifier DWC are 5.9% and 5.1% less than those of the conventional system, respectively. The economic evaluation indicates that the side-rectifier DWC requires 57% less investment and 10% more utility cost than the conventional system. However, low feed pressure used in the side-rectifier DWC saves the compressor cost of 5.1 times the investment cost and the electricity cost of 1.8 times the total utility cost of the high-pressure conventional system.

Thermodynamic design of natural gas liquefaction cycles for offshore application

A thermodynamic study is carried out for natural gas liquefaction cycles applicable to offshore floating plants, as partial efforts of an ongoing governmental project in Korea. For offshore liquefaction, the most suitable cycle may be different from the on-land LNG processes under operation, because compactness and simple operation are important as well as thermodynamic efficiency. As a turbine-based cycle, closed Claude cycle is proposed to use NG (natural gas) itself as refrigerant. The optimal condition for NG Claude cycle is determined with a process simulator (Aspen HYSYS), and the results are compared with fully-developed C3-MR (propane pre-cooled mixed refrigerant) JT cycles and various N2 (nitrogen) Brayton cycles in terms of efficiency and compactness. The newly proposed NG Claude cycle could be a good candidate for offshore LNG processes.

Project integrated LNG offloading availability assessment for FLNG

This extended abstract explains a combined heuristic, analytical, and probabilistic process to evaluate LNG offshore offloading availability in combination with facility uptime and commercial drivers such as LNG sales/supply contracts. The heuristic assessment is informed by facility operators’, LNGC masters’, and tug operators’ experiences in offshore offloading and berthing operations. The analytical process includes assessment of met-ocean, mooring, manoeuvrability simulation, model testing and event forecasting methods. Gaps about uncertainties for future predictions are filled by probabilistic Monte-Carlo simulations. The heuristic, analytical, and probabilistic approach, combined with commercial drivers, is put together into uptime assessment to forecast the techno-commercial performance of the facility. The uptime assessment enables: confidence on achievable LNG throughput, the best for facility configuration and size, the best for facility location and facility’s operational expenditures; contractual viability—for LNG supplier and gas off-taker; and, key to terminal performance guarantee to gas off-takers. This process has been developed within INTECSEA during the past six years and has been applied to more than 15 LNG offshore offloading facilities at varying geographical locations. This extended abstract explores the key drivers and describes the effect on those key drivers due to varying location, varying technology, or LNG sales/supply contracting strategy. The key drivers include: achievable LNG throughput, uptime, downtime, demurrage, cargo cancellation, facility downturn, and partial LNG offloading. The process described is specific to side-by-side offloading operations; however, it can also be adapted to standard jetty offloading operations and tandem offloading operations.

Optimal module layout for a generic offshore LNG liquefaction process of LNG-FPSO

Constraints related to offshore projects such as liquefied natural gas floating, production, storage, and offloading (LNG-FPSO) have been considered more important than those in onshore areas because topside process systems are located on the limited hull space. Therefore, the layout of the LNG-FPSO topside equipment shall be designed as multi-deck instead of single-deck, and this layout shall be optimised in order to reduce the area occupied by the topside equipment at the front-end engineering design stage. In this study, an optimal module layout for a generic offshore LNG liquefaction process system is derived, considering the deck penetration of long-length equipment across several decks. By considering the above, we formulate a mathematical model, which consists of 1652 unknowns, 1624 equality constraints, and 1048 inequality constraints. This mathematical model can be regarded as the optimisation problem, in which the number of unknowns is larger than the total number of equality constraints and given variables. To obtain the optimal layout, the minimisation of the total layout cost was defined as an objective function. The optimal module layout was then obtained using a mixed integer nonlinear programming.

Economic Analysis of Liquefied Natural Gas Floating Production Storage and Offloading Plant (LNG FPSO) Using Probabilistic Approach

The global yearning for clean and safe environment coupled with the need of monetizing stranded gas fields to meet the growing demand of Natural gas in the world today has called for understanding of the range of potential for commercial realization of Liquefied Natural Gas Floating Production Storage and Offloading Plant (LNG FPSO). This places a heavy burden on the economic evaluation process which will give the maximum insight into the basis for a decision to invest or not to invest in the LNG FPSO. An economic analysis of 5.2 million tonnes per annum (MTPA) LNG FPSO plant was undertaken. A Monte Carlo simulation method was adopted in this study through the use of Crystal Ball Software. The key uncertainties were represented and their respective impacts on economic viability defined. The deterministic model results obtained from the studies were very impressive with Net Present Value of $2.3 billion at a discount value of 15% and Internal Rate of Return at 32.68%. Probabilistically, 74.96% certainty of having a positive net present value (NPV) and good IRR values far above the hurdle rate for investment in Nigeria was obtained. These clearly showed that LNG FPSO is profitable. Certainty of payback period of not exceeding 5 years was obtained to be 55.89%. Key words : LNG FPSO; Offshore LNG liquefaction; Probabilistic approach; Sensitivity analysis; Economic yardstick

Offshore concrete structures

In the offshore industry there are two possible materials for the construction of the hull of any structure: steel and concrete. Steel is being widely used in the shipbuilding industry for merchant ships, warships, etc. Materials such as aluminium, glass reinforced plastic (GRP) or timber are also used in small units with lengths lower than 100m and with less adverse conditions than in the offshore industry. Nevertheless, some ships/barges have been built of concrete in the past, but these have been rather isolated cases and have not changed the industry practice. During the First and Second World War concrete was used due to the scarcity of other materials, so the series of barges by Alfred A. Yee were a rare exception. Other floating structures were also made in concrete, but they are almost anecdotal. However, the behaviour of these concrete structures, especially in terms of maintenance, has been excellent. Therefore, the fact that concrete has not had an adequate reception so far in shipbuilding does not mean that it will not be the material best suited to the offshore industry in the future. The extra displacement and associated fuel costs in concrete ships have been found to be prohibitive in the past. However the loss of mobility in a concrete hull compared to a steel hull can be perfectly offset by the advantages offered by concrete, as the shipping and offshore industry now have very different priorities. One of the main differences in these priorities is the importance of maintenance and resistance to fatigue, precisely the areas where concrete performs the better. Ships can easily be dry-docked for maintenance and repair, while in the offshore platforms these works have to be done in situ, so maintenance and fatigue are crucial to them. Besides these aspects, concrete has other advantages, according to a number of findings in several studies. This supports the fact that in recent years concrete offshore units have been built proving that in certain cases the benefits of steel are inferior to those of concrete. Concrete gravity base platforms type Condeep have been building since the first unit became operational in 1976, together with a few floating platforms, that have geometry similar to those made of steel (barges, semi-submersibles and TLP type platforms). Offshore LNG terminals and offshore industrial plants utilise emerging concepts in concrete that are lasting for years. The life of these barges can be designed for up to 200 years, such as the floating Nkossa barge, so they can be a good alternative to the construction of these facilities on land, thus avoiding landfills on the coast that degrade the already punished coastline of industrialized countries. The challenge is precisely to optimize their capital costs to compete for an offshore installation against a shore facility. The environment will undoubtedly benefit from this great challenge that lies ahead in the XXI century.

First step in optimizing LNG storages for offshore terminals

The development of new LNG offshore facilities addresses new technical challenges that need to be deeply investigated to overcome the new constraints raised from the offshore operability. One of the key issues concerns the management of LNG storages. As future offshore LNG projects could be implemented in areas with harsh environmental conditions, the motions of the floating structure combined to the design and operating parameters should widely affect the behavior of the LNG inside partially filled tanks. Therefore, the knowledge available from onshore LNG storages has to be completed taking into account the offshore environment. The first concern deals with the production of Boil-Off Gas (BOG) during LNG’s unloading and storage operations under offshore conditions, where specific offshore parameters would contribute in increasing the production of BOG. For that purpose, a new optimized LNG storage process based on an increased operating pressure ( P = 500 mbarg) in the TRITON FSRU’s tanks has been investigated during LNG’s unloading and storage operations with LNG emission. It mainly showed that by operating at 500 mbarg, the production of BOG is nearly 4 times reduced during unloading operations compared to LNG carrier standard operating pressure (100 mbarg) and nearly suppressed during the storage phase. The second concern deals with managing the rollover risk under offshore conditions. In this context, GDF SUEZ performed a pioneer qualitative assessment to highlight the impact of the liquid motion on the rollover mechanisms in the TRITON FSRU’s tanks. The liquid motion completely modifies the mixing mechanisms in LNG stratified layers. The mixing is no longer governed by the molecular diffusion induced by the thermal effects but by the dynamic flow effects induced by the fluid wave movement into the layers. Moreover, this assessment showed that the time needed for a stratification to evolve up to a complete mix is severely reduced compared to the onshore LNG storage while the assessment of the induced BOG peak depends as usual on the energy stored in the stratification when being mixed and could be of the same order of magnitude as for onshore rollover.

WAVE HEIGHT DISTRIBUTIONS IN SHALLOW WATERS

In shallow waters the wave height distribution significantly differs from Rayleigh distribution during extreme wind&#x0D; conditions. The EurOtop manual (Pullen et al. 2007) recommends the use of a composite Rayleigh-Weibull distribution proposed by Battjes and Groenendijk (2000) in order to describe the wave statistics in shallow waters. A test of this recommendation by using wave measurements with continuously operated radar level gauges at three different sites at the German North Sea coast for comparison revealed the necessity for a change in the parameterization given in the EurOtop manual.&#x0D; &#x0D; &#x0D; References&#x0D; &#x0D; Barjenbruch, U., S. Mai, N. Ohle, and U. Mertinatis. 2002. Monitoring Water Level, Waves and Ice with Radar Gauges, Proceedings of the Hydro 2002 Conference, DHyG, 328-337.&#x0D; &#x0D; Barjenbruch, U., and J. Wilhelmi. 2008. Application of radar gauges to measure the water level and the sea state, Proceedings of 31st International Conference on Coastal Engineering, ASCE, 687-695.&#x0D; &#x0D; Battjes, J.A., and H.W. Groenendijk. 2000. Wave height distributions on shallow foreshores, Coastal Engineering, 40, 161-182. http://dx.doi.org/10.1016/S0378-3839(00)00007-7&#x0D; &#x0D; Burcharth, H.F., P. Frigaard, J. Uzcanga, J.M. Berenguer, B.G. Madrigal, and J. Villanueva. 1996. Design of the Ciervana breakwater, Bilbao, Advances in coastal structures and breakwaters, Thomas Telford, London, 26-43.&#x0D; &#x0D; Forristall, G. 2008. Offshore LNG terminal designs must overcome complications of shallow water, Oil &amp; Gas Journal, 106(43).&#x0D; &#x0D; IAHR Working Group on Wave Generation and Analysis. 1989. List of Sea-State Parameters, Journal of Waterway, Port, Coastal and Ocean Engineering, 115(6), pp. 793-80 http://dx.doi.org/10.1061/(ASCE)0733-950X(1989)115:6(793)&#x0D; &#x0D; Klopman, G., and M.J.F. Stive. 1989. Extreme waves and wave loading in shallow water, Proceedings of E&amp;P Forum Workshop: Wave and current kinematics and loading, Paris, Oct. 25-26.&#x0D; &#x0D; Longuet-Higgins, M. S. 1952. On the Statistical Distribution of the Heights of Sea Waves. Journal of Marine Research, 11(3), 245-266.&#x0D; &#x0D; Mai, S. 2008. Statistics of Waves in the Estuaries of the Rivers Ems and Weser - Measurement vs. Numerical Wave Model, Proceedings of the 7th Int. Conf. on Coastal and Port Engineering in Developing Countries COPEDEC, CD-ROM.&#x0D; &#x0D; Nelson, R.C. 1994. Depth limited design wave heights in very flat regions, Coastal Engineering, 23, 43-59. http://dx.doi.org/10.1016/0378-3839(94)90014-0&#x0D; &#x0D; Pullen, T., N.W.H. Allsop, T. Bruce, A. Kortenhaus, H. Schuttrumpf, and J.W. van der Meer. 2007. EurOtop - Wave Overtopping of Sea Defences and Related Structures: Assessment Manual, Die Kuste, 73, 193 pp. (online:

Developing Aussie home-grown talent in an international market

With the current skills shortage in the engineering profession and the need for more experienced engineers, it is important for Australian engineering companies to not only rely on importing skilled engineers from overseas to fulfil current day demands, but also to focus on developing young Australian engineers for the future. Aker Solutions Australia has implemented a training and development program for its employees by seconding them into the head office in Oslo, Norway for both technical and personal development. The program provides many positive outcomes for both the company and the employees including: knowledge transfer and alignment between the international offices, developing and improving the talent of Australian engineers, improving communications between the offices and providing the Oslo office with much needed resources. The program was initiated in 2006 and so far nine employees have been sent across the globe for training. In this time the employees have had the opportunity to work on new technological developments in gas processing, advanced concept development studies and large scale engineering, procurement and construction (EPC) projects. Working internationally has also provided Australian engineers with a chance to interact with a number of skilled people from diverse backgrounds, learn new languages and embrace different cultures. The program to date has had much success, with both clients and the Aker Solutions office in Norway requesting continuation of the Australian engineers’ services while one of the engineers—Jacqui Driver—won best paper at the 2007 APPEA conference for her work in Oslo on novel offshore LNG solutions.

A liquefied energy chain for transport and utilization of natural gas for power production with CO 2 capture and storage – Part 3: The combined carrier and onshore storage

A novel energy and cost effective transport chain for stranded natural gas utilized for power production with CO 2 capture and storage is developed. It includes an offshore section, a combined gas carrier and an integrated receiving terminal. The combined carrier will transport liquid carbon dioxide (LCO 2) and liquid nitrogen (LIN) outbound, where natural gas (NG) is cooled and liquefied to LNG by vaporization of LIN and LCO 2 onboard the carrier. The same carrier is used to transport the LNG onshore, where the NG can be used for power production with CO 2 capture. The combined carrier consists of 10 cylindrical tanks with a diameter of 9.2 m and varying lengths from 14 to 40 m. The total ship volume is 13,000 m 3. Assuming 85% capture rate of the CO 2, the maximum ship utilization factor (SUF) is 63.4%. Due to the combined use of the storage tanks, the SUF is decreased with 1.4% points to 62%. The ship is equipped with a bi-directional submerged turret loading for anchoring and loading of NG and unloading of CO 2. Two ships can deliver NG to and remove CO 2 from a 400 MW net power plant, and still obtain continuous production of LNG offshore without intermediate storage. The investment cost for each gas carrier is 40 million EUR giving total transport cost of 16.9 EUR/tonne LNG. The cost for the offshore transfer system is 6.6 million EUR per tonne LNG, whereas the cost for onshore storage and loading system is 3.1 and 0.8 million EUR per tonne LNG, respectively. The total specific costs for the ship transport, including onshore storage, loading shipping and offshore unloading are 27.5 EUR per tonne LNG for a roundtrip of 5 days, including voyage, production of LNG, unloading, connecting and berthing.

Offshore Natural Gas Liquefaction Process and Development Issues

Summary Liquefied natural gas (LNG) has yet to be deployed in the development of offshore fields in spite of several detailed studies completed and offshore technology development demonstrating its technical feasibility. The perceived risks associated with deploying unproven technology in a high construction cost and volatrile gas price environment have so far inhibited offshore liquefaction projects. The potential deployment of such technologies is of paramount importance considering the massive volumes of natural gas currently deemed as "stranded" and the exploitation of which is compelling not only because of the inherent economic benefit but also because of the otherwise adverse impact on oil production. It is conceivable that deep water offshore locations may contain quantities of natural gas rivalling those of onshore locations. Such a statement cannot even be confirmed because drilling for offshore natural gas reservoirs, expected to be found considerably deeper than oil reservoirs, has been unattractive exactly because of the absence of coherent exploitation strategies. If anything, the mere presence of large natural gas deposits even in the form of solution gas in oil is now often considered as largely undesirable because of the cost of just handling non-monetized natural gas. This paper discusses potential offshore LNG processes and reviews natural gas liquefaction cycles in the context of compactness, ease of operation, process safety, and efficiency. Particular attention is paid to the lower-efficiency turboexpander processes for plant capacities up to 3 million tonnes per annum (MTPA, approximately 0.43 Bcf/d). These cycles offer several advantages over the alternative optimized cascade and mixed refrigerant (MR) liquefiers for offshore applications.

NOVEL OFFSHORE LNG SOLUTIONS

The demand to process associated and stranded gas is growing and there is increasing commercial interest in offshore LNG production. Limitations in available land and carrier access, safety and environmental considerations and difficult onshore permitting have created an interest in locating LNG terminals offshore. These factors are providing incentives to develop solutions and the technologies required to transfer the liquefaction and re-gasification segments of the LNG chain to offshore locations. Some of the hurdles that need to be overcome are associated with equipment size, weight and layout, energy consumption, the marine environment and, for floating facilities, the moving environment. All of these aspects need to be addressed to produce an overall design that meets technical, commercial, safety and environmental requirements. This paper presents some recent developments in offshore LNG solutions for floating and fixed offshore LNG production and offshore LNG re-gasification terminals. Specific case studies for each facility are: a floating LNG production facility for the Nnwa-Doro gas field offshore Nigeria; a fixed offshore liquefaction facility in the Arctic region; and, the Adriatic LNG receiving terminal located offshore Italy. Information about an alternative method of transporting natural gas—called heavy liquefied gas (HLG)—which has some specific advantages over traditional LNG, is also presented. For each case study, design, construction, cost and schedule are discussed where applicable.