OTC 19845
The LNG Producer - A Generic Design with Great Adaptability
Wouter Pastoor, Kristine Lund & Trym Tveitnes, FLEX LNG
Copyright 2009, Offshore Technology Conference
This paper was prepared for presentation at the 2009 Offshore Technology Conference held in Houston, Texas, USA, 4-7 May 2009.
This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents ofthe paper hace not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Cottference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibitedPermission fo reproduce Irr print is restricted to an abstract of not more than 300 words; iflustrationo may not be copied. The abstract must contain conspicuous acknowledgment uf OTC copyright.
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Abstract
The LNG Producer is a floating, ship-shaped vessel that can produce LNG, condensate and LPG from stranded and/or associated gas fields offshore. FLEX LNG has four hulls on order and has an EPCIC contract for the topsides of the first vessel. A well-defined set of design principles and criteria have been essential to develop the LNG Producer. In addition the development of the design is strongly supported by market analyses, client feedback and technology evaluations. The final design is neither an evolution from the LNG Shipping industry or the Offshore Oil&Gas industry nor a marinization of a land-based liquefaction plant but a dedicated unit combining the best of these industries. This paper describes the design process and the resulting basic design. Particularly the generic character of the design is described and the adaptability to serve a large range of gas fields, with all kind of project and client specific requirements and conditions. The paper assists both engineers and project developers to consider floating LNG production for a given offshore or onshore gas field.
Introduction
The LNG industry is growing at a rapid pace and medium to long-term forecasts predict a shortage of LNG supply in a few years time. With the huge amount of stranded gas fields and associated gas the introduction of offshore LNG production, or often referred to as Floating LNG (FLNG), can reduce the gap between supply and demand. The key arguments supporting floating LNG production are the competitiveness against land-based plants, the short lead-time, the adaptability for field specifics, the redeployment feature and the use of existing LNG and FPSO construction facilities at shipyards.
FLEX LNG has been pioneering the development of small to medium sized floating LNG production vessels since 2006. The rapid development by FLEX LNG has been supported by a large amount of engineering studies, a close cooperation with customers and an early order at Samsung Heavy Industries (SHI). Currently, FLEX LNG has four LNG Producer hulls ori order at SHI. Each hull has a storage capacity of 220,000 m3 for LNG and condensate or alternatively the inclusion of LPG. These LNG Producer hulls are not just bare steel hulls but comprise a complete LNG Producer vessel except for the topsides. Only for the first hull have the topsides been ordered. In September 2008 FLEX LNG signed a turnkey, lump sum
Engineering, Procurement, Construction, Integration and Commissioning (EPCIC) contract with SHI for the topsides and the hull. Consequently, for the first vessel SHI is fully responsible to construct the hull and the topsides, the integration of both and the commissioning of the LNG Producer at the both the shipyard and offshore on site.
Design development
FLEX LNG has gone through a design process which has resulted in the current LNG Producer design. Over time the initial vessel design has increased both in storage size and production capacity. Moreover condensate and LPG extraction, stabilization, storage and handling systems have been designed. All the design and engineering that have been done were essential to develop an optimal generic design. This generic design is the starting point for every project.
The overall design principles that have been used in this development process were: Maximum use ofproven and robust technologies
In order to enhance the project success a maximum use of proven and robust technologies has been followed. Commitment to safety - implement the industry 's best safety practices
The LNG industry has a great safety record. When developing FLNG as a new branch to the LNG industry safety shall be on top of the agenda in design, construction and operations.
Simplfii the design and remove unnecessary complexity
Moving offshore the importance of robust, reliable, maintainable and inherently safe systems becomes more important compared to other criteria like for example efficiency.
2 OT 19845
Market focused engineering - quickly adapting to the client needs
Many of the clients have a large knowledge base of liquefaction andlor offshore floating production. Consequently, these have provided very valuable input on important design choices that were made in the early phases.
Standardization of generic topsides
Irrespective of any project a large amount of pre-treatment, liquefaction and utility systems will be the same. Standardizing this part will provide cost savings for both CAPEX and OPEX and support fast-track developments. Field spec(fIc topsides on dedicated modules
The field specific requirements for the topsides may vary substantially depending on the project. By introducing the field specific module(s) this can easily be handled as a dedicated design and engineering task.
Adaptabilitvforjìeld/client specific requirements
No field is the same, no client is the same and no shelf state has equal regulations. Reviewing these typical requirements, sufficient adaptability is built into the LNG Producer to accommodate these.
C'ombining the best of LNG Shipping & Offshore Production & Onshore liquefaction
The LNG Producer is an evolution of the LNG shipping, the offshore oil production and land-based liquefaction industries. All these areas are vital to develop this new branch to the LNG industry and this is reflected by the experience and background of the people in FLEX LNG.
A large number of design, engineering and analysis studies have been conducted by FLEX LNG and contractors to support and guide the development of the LNG Producer. Pre-engineering work was done for the topsides. Subsequently a tender process for the topsides FEED contract was conducted which included pre-engineering work by all these bidders. Two bidders were selected and conducted a parallel FEED for the topsides of the first vessel. SHI developed a full shipbuilding
specification for the vessel and marine systems. In parallel to these engineering phases a large series of other studies were conducted, e.g.
Formal Safety Assessment
Model basins tests of side-by-side offloading Bulk CO2 removal study
Dynamic Process Simulation study HAZIDs / design review workshops Independent3rdparty verification studies Due diligence assessment by potential offtakers
Throughout 2008 a large number of industry players have conducted detail design reviews and due diligence sessions of the LNG Producer design. A lot of the comments and questions have been used to support the ongoing design and engineering work by FLEX LNG and its contractors. Based on this review process with clients FLEX LNG is fully comfortable with the current design and the key technical solutions that have been chosen for the LNG Producer.
The LNG Producer basic design
The main technical areas of the LNG Producer are described in this section.
Hull and marine systems
The main dimensions of the LNG Producer are:
Length overall 336 m
Length between perpendiculars 328.0 m
Breadth, moulded 50.0 m
Depth to upper deck, moulded 31.6 m
Scantling draught, moulded 14.5 m
Transit draught, moulded (without cargo) 9.5 m
LNG storage capacity 170,000 m3
Condensate storage 50,000 m3
(Alternatively LPG may be included)
The vessel is a, self-propelled, double-hull vessel with a ship-shaped huliform designed for optimal and low forward speed. On the foreship the accommodation is located with a berth capacity of 120 beds. This can be increased to 150 berths during large maintenance and overhaul periods by adding temporary beds. On top of the accommodation is a heli-deck sized for a Super Puma with or without refueling. Below the accommodation is a machinery room with auxiliary machinery systems. Behind this area is the turret compartment with ballast tanks on the sides. The turret is an internal disconnectable turret with the swivel stack located inside the compartment. Aft of the turret compartment is the first condensate tank, 4 identical LNG cargo tanks and then the second condensate tank, including slop tanks. On the aft ship is the engine room with the power generation, seawater cooling systems and other auxiliary machinery. Two aft-mounted azimuthing thrusters of 4.5MW each give the
vessel a design speed of 8 knots. Besides propulsion these thrusters are needed to provide heading control of the vessel for offloading operations and to create a lee side for supply vessel operations.
The machinery and engine room include all the standard support for the vessel, e.g. sewage treatment, fresh water, AC etcetera. In addition the bulk of the utilities for the topsides are provided by these vessel machinery systems. Consequently, a range of systems have been upgraded to provide these utilities, e.g. compressed air, nitrogen, fire water, electric power. Crane coverage is provided for the topsides deck, the STP compartment and offloading equipment. A material handling study was done to define the lifting and lay-down requirements. Without the need for dry-docking the vessel and systems shall be
maintained, repaired and overhauled on site, which set specific requirements for these cranes.
The hull is designed and constructed in compliance with the DNV Ship Classification Rules. Effectively the hull is thus designed for 20 years North Atlantic operations (max Hs = 125m). For offshore production applications in benign environments this is sufficient considering both ultimate and fatigue strength. The material protection and paint schemes are
upgraded allowing the vessel to operate on site for the field life without the necessity of dry-docking.
Extensive tests and trials will be conducted at supplier's facilities, at the shipyard and during sea trials and gas trials. An important test will be liquefaction tests. SHI and FLEX LNG are developing a full test package for testing the liquefaction system before the transit to site. This test will be done using a regasification skid. The skid will temporarily be installed on the LNG Producer and will regasify LNG, which is then provided as pressurized natural gas to the liquefaction modules, which liquefy the gas. Of course conducting the liquefaction test before transit and in close proximity to the shipyard is a very important system test, which is strongly supported by all clients.
leid specific
modules / design Cooler utilitieLh-
'on
mpressor
dule
Pre-treatment
en ericFigure 1 Illustration of the LNG Producer with main generic and field specific modules LNG cargo tanks and systems
The LNG is stored in four identical IHI-SPB tanks, categorized as 1MO Type B with a total storage capacity of 1 70,000m3. The IHl-SPB containment system is chosen as this system provides a large flat deck for the topsides and secondly this system is a robust design which does not have any sea state limitations for partially filled conditions. Alternatively, the well-proven Moss design could have been used, as this allows for partially filled operations. However there would be far too little deck space for the topsides. Another alternative, the membrane technology, could provide sufficient deck area, but will impose sea state restrictions for partially filled operations. As a solution the membrane tanks could be divided into smaller sized tanks, which will reduce the sloshing in the tanks however the cost-benefit for using the membrane technology is then lost. Moreover a membrane tank cannot simply be divided in two by a bulkhead but will need a cofferdam and hence the high space
utilization by the membrane technology is lost as well.
Each cargo tank will be divided in two compartments, separated by a centerline bulkhead. In addition a transverse swash bulkhead is installed. Effectively, these bulkheads will eliminate any sloshing motion. Polyurethane foam is mounted on the outside of the tanks. The SPB tanks will be constructed of stainless steel 304 and the production will be conducted in a dedicated construction hall, such that any dirt, dust or weather influence is kept outside. In order to prepare for the production
a large mock-up model was built in early 2009. This mock-up is a block with a weight of 75 ton and with 1.7 km weld length (butt and fillet). This mock-up is an actual sized block from the bottom and centre of a cargo tank. This block was selected as it is a combined structure (bottom support, stringer, swash BHD, frame section) and it provides all elements to be checked by the construction teams. Many aspects were checked in order to prepare all the necessary procedures for the construction phase. Of course a key focus was on the quality and accuracy of welding, however many more aspects were duly verified like lifting arrangements, plate handling, cutting, cleaning, repair methods, distortion checks, sequences of tasks etcetera.
Complete LNG cargo handling systems are provided to conduct all necessary tank operations as for an LNG carrier. In addition the systems are designed to accommodate simultaneous production and unloading as well as tank inspection during production.
Figure 2 Illustration the SPB tank inside an LNGP, the 74 ton mock-up and actual mock-up construction at SHI Process and topsides design
The topsides design is separated in two distinct sections, the generic plant and the field specific plant. The generic plant is designed to treat a wide range of varying hydrocarbon content feed gas compositions, roughly from 85-99% methane. It also removes set quantities of acid gas (CO2 and H2S), water and mercury. The field specific plant is specifically designedfor a given field(s). The topsides are designed in modules with the key equipment and systems divided as follows:
An impression of the vessel with the main modules for the field specific and generic part is shown in figure 1.
For a typical feedgas flow with 93% to 96% methane the nameplate production capacity is 1.7 mtpa. Part of the feedgas is used as fuel. The shrinkage is defined as a percentage from the feedgas flow by subtracting the LNG production into the tanks minus the inlet feedgas flow. Typically this shrinkage is around 12 percent.
The process system of the generic plant consists of the following modules: Pre-treatment module
Liquefaction module Cooler utility module GT and compressor module
The liquefaction process is a two-train system, which operates independently from each other, i.e. 2 x 50%. The pre-treatment is a single 1x1 00% system. However many sub-systems, drives, controllers etc are redundant. A dual nitrogen expandercycle
Generic Plant Field-Specific Plant (example sub-systems)
Gas turbines and compressors Inlet separation and slug catchers
Cooler utilities Condensate handling systems
Liquefaction and HHC control LPG handling systems Generic pre-treatment module HHC stabilization systems
Produced water treatment systems Test separation
Production metering systems Condensate export
Chemical injection systems Feed gas heating/cooling Feed gas recompression Bulk CO2 removal
Etc.
has been selected for the LNG Producer, as this is most suitable for the required production range and for an offshore application. Important arguments to choose this technology are:
Inherent/v safe
The nitrogen expander is significantly safer than liquefaction technologies using flammable refrigerants (e.g. Cascade or MR). For land-based plants increasing spacing between systems is a design parameter to achieve acceptable safety levels. Since a floating facility has limited deck area for the plant maintaining acceptable safety levels cannot be done by large spacings.
Minimum space, weight and equipment count
Even without safety consideration, the dual nitrogen expansion cycle requires less area and weighs less than MR type systems and has a lower equipment count as well.
Simple controllability
In comparison to Cascade or MR systems, the nitrogen expansion system is a more simple process system with straight forward controllability.
Quick start-up and shut-down
The nitrogen expansion system allows quick start-up and shut-downs, which in an offshore environment is most desirable as this may happen more frequent and should therefore not cause longer interruptions then necessary. Robust to motions
The nitrogen expansion system has one single refrigerant operating in the gas phase only and is therefore hardly affected by ship motions.
Insensitive to large feedgas range
A large feedgas compositional range can easily be processed by the nitrogen expansion system with high efficiency. MR type processes are designed for a given feedgas composition as the refrigerant evaporation ideally matches the LNG condensation. For varying feedgas conditions the nitrogen expansion can have higher efficiency than an MR system.
Cheap refrigerant
Nitrogen is easily provided by onboard installed nitrogen generators at low costs.
An important reason to choose a more complex MR or Cascade system is to have a higher efficiency. Indeed the dual nitrogen expansion system is less efficient, however from an overall perspective the efficiency is not the prime driver and weight, space, robustness, simplicity, annual availability and CAPEX are more important for an offshore application. Furthermore the development of the dual nitrogen expansion system is ongoing with further efficiency improvements.
The main nitrogen compressors are directly driven by LM6000 aeroderivative gas turbines. Both gas turbines are equipped with waste heat recovery units (WHRU) providing 2xl00% heat for topsides use. These WHRU use thermal oil as heating medium. The high efficiencies of these gas turbines in a direct drive configuration offset the lesser efficiency of the nitrogen process. The gas turbines use natural gas as fuel. Condensate burning has been studied and may be used on projects, but for most projects the arguments are not in favor of this option. With a price premium for condensate over LNG per ton it makes most sense to sell the condensate instead of burning it as fuel. However for projects where there is very little condensate it may be attractive to use this as fuel and by that reduce complexity on the topsides and simplify the offloading operations and logistics. The whole GT/compressor module is provided as an integrated package by a single supplier. Careful attention is being paid throughout design, engineering, construction and testing of this direct drive arrangement. The alternative could have been to use electric drives. In an early engineering phase this was worked out but abandoned for several reasons. First of all, choosing electric drives introduces a lot more sensitive and costly equipment, both in terms of CAPEX and OPEX. Secondly, this configuration gives a reduction of more than 5% on the production capacity for the same GT drives. Electric drives are more efficient at lower load levels, but in principle the plant shall run at maximum capacity and turn-down is not a normal operational requirement. Electric drives have gained more popularity due to significant developments in electronics, the availability of cheap' electricity and because of environmental considerations when "green" electricity is available. These arguments do not apply for an offshore floating plant.
There will be no flaring or venting of un-burnt hydrocarbons from the topside process plant during normal operations. The pressure relief and vent system is designed to safely dispose gases to the atmosphere in situations that require evacuation of such as these could pose a risk to the ship, equipment and personnel. The systems are designed to dispose of wet or dry fluids to separate warm gas or cold gas closed collection systems discharging to separate high-pressure/low-pressure/warm!wet flares and the venting of gases directly to the atmosphere, depending on the fluid properties, molecular weight, and temperature.
Power generation
A lot of energy is needed for the liquefaction process, of which the bulk is provided by mechanical drive of the main nitrogen compressors. All other electric power is provided by Dual Fuel Diesel Electric generator sets (DFDE). In total four engines are installed providing a shaft power of 11,400 kW each. The DF engines have become the preferred propulsion choice for medium sized LNG carriers (up to I 70.000m3). In normal operation the engines run on natural gas provided by the feedgas and
6 OTC 19845
boil-off gas. The required pressure of the natural gas fuel is only a few bars, which eliminates the need of large BOG compressors for other drives like gas turbines. Only 1% pilot fuel (MDO/MGO) is injected. In the absence of natural gas the engines can run 100% on MDO/MGO. Sufficient sparing is incorporated also for high demand cases during offloading, while producing and maintaining heading control of the vessel with the thrusters. Finally it should be noted that these engines have a low cost per MW both in terms of CAPEX and OPEX.
Turret mooring system
The vessel is equipped with an internal disconnectable turret mooring system, which is the Submerged Turret Production (STP) system from Advanced Production and Loading (APL). A submerged buoy is positioned in the mating cone in the bottom of the ship and locked by hydraulic locking devices. The turret is inside the buoy and supported by a lower and upper bearing in the buoy. Therefore all mooring loads are transferred by the buoy and mating cone into the ship structure.
Incorporating the turret inside the buoy is different from other turret suppliers for which turrets extend over the ship's depth. The risers and umbilicals are hung-off at the top of the buoy. On top of the buoy and below the swivel stack are valve,
manifold and pigging arrangements. The swivel stack is positioned on a skid such that it is positioned to the side during connecting and disconnecting. On top of the STP compartment are explosion relief panels and a large hatch. The hatch provides access for materials and equipment and for the ropes to pull in the buoy. On deck a large winch is installed to pull in the buoy during connections. A heave compensator can be installed to ensure that buoy connections can be performed in
higher sea states.
The STP system is very similar to the Submerged Turret Loading (STL) system and both have been in use on a large number of loading and production units. Especially the SIL system has a successful track for crude loading offshore by shuttle tankers where this system has experienced well over 1100 connects and disconnects only in the North Sea.
The STP system as designed for the LNG Producer has been sized for a broad range ofprojects in the portfolio. The STP compartment, buoy and swivel stack have been dimensioned to accommodate up to 6 risers (4x12" ID and 2x6" ID) and 6 umbilicals. Alternative combinations with e.g. 8" or 10" risers are fully feasible.
Although the STP for the LNGP has generic features there will be field specific changes for every project. In any case the inlet arrangement with the risers, umbilicals, valves and swivel needs to be reviewed. So far there has not been a need to re-size the buoy and STP compartment.
Offloading
The offloading of the products is done by liquid transfer to a shuttle tanker. For benign environments the LNG can be discharged in a side-by-side (SBS) configuration. For this configuration the shuttle LNG carrier is moored alongside the LNG Producer and offshore marine loading arms are used to discharge the cargo to the standard midship manifold on the LNG carrier. An important reason for choosing this configuration is that standard LNG carriers can be used to ship the cargo to the market. In case of a tandem offloading operation the LNG carrier would need a bow loading arrangement, which makes it a dedicated LNG carrier and thus it would reduce the trading flexibility. Moreover SBS is done on a daily basis for many other products and loading arms are well-proven equipment on (LNG) terminals, which provided a good basis to develop these for an offshore application.
The main equipment that is installed on the LNG Producer are the offshore marine loading arms, the SBS mooring system and the fendering systems. Berthing assistance systems are also used to support the approach, berthing and departure of the LNGC.
Both fore-cast and real-time wave, wind and current measurements/predictions are used to assist the crew in the planning of the operations.
The LNG Producer can accommodate LNG carriers of both membrane and spherical type. The sizes can vary from 125,000in3 up to 155,00 m3. Other vessels, outside this range, can most likely berth as well although a mooring compatibility needs to be verified.
As the SBS offloading of LNG is a novel operation a large amount of design and engineering work has been done to develop the systems and procedures, like:
mooring arrangement drawings,
mooring material and line property selection berthing and approach procedures
numerical SBS simulations
approach and berthing simulations (fast-track and real-time) HAZID
And a very important part has been the physical modeltesting in the offshore basin at the Maritime Research Institute Netherlands. Some key features of this testing are:
All models were at 1:50 scale and with a waterdepth of 150 m
Both Moss and membrane LNGCs have been tested alongside the LNGP
Fenders were modeled by lever arms with springs, fender friction was not modeled as part of the tests Passive and non-passive (thruster assisted) tests have been conducted
Tests have been conducted for two loading conditions i.e. LNGP-loaded & LNGC-ballast and vice versa A variety of wind wave, swell wave, current and wind combinations and directions have been tested Cases beyond acceptable levels were tested for the purpose of tuning a numerical model
Single body regular and irregular motion and transit tests were conducted
e Single point moored survival tests were conducted
Basic regular tests, decay tests and white noise tests were done for the purpose of tuning a numerical model LNGC drift off tests were included
Broken SBS mooring line tests were included
Figure 3 Illustrations of thrusters, fender and mooring line instrumentation and a drift-off test case
The key findings from this test program were:
Side-by-side offloading is feasible up to 3 m H in non-collinear sea and swell environments. Of course the sea and swell directional deviation is critical to the performance and one shall be careful using a single wave height criterion.
Heading control can significantly reduce both mooring line loads and relative motions.
Ifa mooring line fails in up to 3 m ft. the results show that the other lines can redistribute the loads so that the SWL of the mooring lines is not exceeded. Also motions are still within the safe operating envelope of the loading arms. The safe working load of the mooring lines is exceeded before reaching limiting conditions for the fenders or the operational envelope of the loading arms. This is preferred as it is a fail-safe approach.
Results will improve with the LNGP increased in length after including a 50,000 m3 condensate storage tank. This is mainly a result of a better mooring arrangement.
After the modeltests MARIN has done detailed analysis to develop a tuned numerical model of the LNG Producer for SBS simulations. Currently, this model can provide a first assessment of the offloading availability for a given site with its specific metocean conditions.
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Classification
The LNG Producer is built according to the DNV Rules for Ships with the topsides being Classed following the DNV Offshore Standards. Furthermore a gap analysis has been done for the hull and marine systems to identify all gaps between the DNV Ship Rules and the DNV Offshore Standards. All necessary design changes have been implemented such that the design will fulfill the requirements from the DNV Offshore Standards. Needless to say that many more design upgrades have been implemented to ensure the vessel and systems are able to operate for the field life, which in most cases is longer than the 5-year docking period for Ship Classed vessels. Typical design upgrades are coating, blanking devices for intakes/chests. underwater dernountable thrusters, upgraded crane specifications, upgrade accommodation etc.
As the LNG Producer combines complex equipment on a novel vessel a close dialogue with the Class Society has been important to get quick support and feedback. Design reviews and HAZIDs have therefore been conducted with Class and DNV has issued an Approval in Principle for the LNG Producer design. Currently, DNV is conducting the plan approval for the first vessel.
Safety in design
One important question that all potential clients have in the earliest phases is about the safety levels of the LNG Producer. Consequently, FLEX LNG decided very early to conduct a full Formal Safety Assessment (FSA) despite the fact that the various design parameters were not fully engineered yet. This lack of input information was circumvented by defining worst case scenarios or using other conservative assumptions. The FSA was conducted by an external safety consultancy, in compliance with the DNV OSS-309 and OS-A 101 requirements and it was reviewed by DNV Class. The scope covered the whole vessel and included the side-by-side operations as well.
The key fmdings of the FSA study were:
Explosion pressures were determined and are incorporated without difficulty in the design of the various structures.
Protection was added of supporting structure (stools) for the topside modules against cold LNG exposure and
following jet/pool fires
Design values for dropped objects were determined and incorporated without difficulty in the design of the various
structures.
The overall lay-out and risks were within acceptable criteria
The height of the flare stack was acceptable (85m from main deck level)
FLEX LNG has designed the escape, evacuation and life savings systems in close cooperation with the safety consultants and the Class Society. Currently, the vessel has two escape routes on both side of the ship sides to safe areas, either the
accommodation or alternatively the far aft of the vessel. Free-fall life boats are installed on both these locations and the sizing is in full compliance with the given safety requirements.
In addition to the FSA, a range of other safety related tasks have been conducted, like HAZID's, HSE philosophies, Safety Integrity Level analysis, safety in operations study, etc.
Having progressed on a variety of projects and with a more mature technical design the FSA was updated in early January 2009 by including also the following aspects:
Update FSA to account for latest technical and operational design basis Conduct explosion simulations
Conduct an Escape, Evacuation and Rescue analysis Determine and assess individual risks
Determine ALARP levels
For any new project the existing FSA will form the basis, which would require an update study to reflect the actual design, the site specific conditions, the client requirements and local regulatory requirements.
Adaptability
The LNG producer design has been developed with a generic approach but maintaining full design flexibility to adapt the vessel and topsides to the specific requirements for a given project. The main items for which the LNG Producer needs to provide sufficient design flexibility are the following:
Reservoir specflcs
As a large range of gas compositions with associated pressures and temperatures is possible. This has the largest impact on the inlet arrangements and the field specific topsides module(s). The field specific topsides module will be purposely designed to make sure the feedgas is properly treated such that the feedgas into the liquefaction part will meet the set criteria. Moreover the internal equipment of the STP compartment can be adapted to meet the field specific requirements.
Field development plan
Since the basic LNG Producer is designed for 20 years operations a long field life is no showstopper. In addition the STP system can accommodate a large range ofriser and umbilical configurations such that initial and future production plans can be facilitated. And since the field specific topsides module will be purposely designed it can incorporate any subsea control and flow assurance requirements there may be.
Metocean and site specfìcs
In principle the water depth and soil conditions at the site do not affect the floater. They have a major effect on the mooring, the risers and buoy design, but this is anyway purposely designed for every project. The metocean
conditions are very important as these may affect a large range of items like structural strength, offloading operations, process systems, efficiencies, etc. Design changes because ofmetocean criteria may require upgrades ofthe LNG producer design, including the generic part. Usually these can easily be accommodated for the hull or generic parts. Especially harsh environments may require several changes to the generic parts of the LNG Producer, like
strengthening, upgraded material qualities, winterizations, wind shields, improved insulations, tandem offloading instead of SBS, etcetera. Nevertheless the generic design is to a large extent designed for rough conditions. For example the generic topsides are designed to operate in up to 8 meter significant wave heights.
Local regulations
Local regulations may comprise requirements from the environmental bodies, the local or federal government, the petroleum board, the public, interest organizations, local fisheries or other neighboring business. For most projects these local regulations require a detailed review of the safety and environmental criteria as a start. Secondly, a careful review is needed to identify all permits and approvals that are needed and the roadmap to achieve these. In addition an early local presence may enhance the support for the project and likewise the project success.
Client requirements
Every client has its own preferences whether that relates to technologies, operations, maintenance or safety. Such requirements may result in minor changes to the generic parts, but they are normally easily incorporated. Depending on the end market, the product specifications may vary. In order to accommodate this requirement the generic part of the topsides can produce a wide range of product specifications whereas the field specific topsides can be designed such that the required condensate or LPG specifications are met. Finally the client or the offtaker may wish to use
non-dedicated shuttle carriers to pick up the cargoes in order to maintain good trading flexibility. Most likely the offloading of condensate or LPG is done by a tandem offloading system with a floating hose. The compatibility of such a system with the trading fleet is very good. Furthermore in benign waters the LNG is most likely discharged to an LNGC in an SBS arrangement. As part of the LNGP design work both Moss and membrane type LNG carriers between 125,000 and l55,000m3 are fully qualified to berth, moor and discharge at the LNGP facility.
When studying these various items it is clear that the most important changes, that may be needed, to adapt the generic LNG Producer design are the following systems:
Turret inlet and swivel arrangements Field specific module(s)
Safety equipment and systems Upgrades of generic parts Offloading equipment
Based on the project developments with various clients it is demonstrated that the generic approach is preferred as most changes can be accommodated. Moreover projects which may consider a change of the production or storage capacity are rare.
Project development
Developing a potential project from initial contact to an FID can be done in an infinite number ofways. But irrespective whether the project has a strong commercial focus at the start or whether it begins with pure technical clarifications the project development phases have some common phases until FID. Typically these are characterized by a concept, a pre-FEED and a FEED phase. An illustration of such a development timeline is shown in the figure below.
lo
The LNGP generic approach and parallel LNGP projects provide important benefits for new projects
thw development costs Fast track development
High reliability of design and engineering in early phases High cost accuracy in early phases
GP dataroom review Concept phase
Detafled project date
Concept alternatives Outline specifications General drawings
PFDs
Utility check
CAPEX & OPEX
Project economics Regulatory /permitting road ma p Risk identification Pre-FEED scope Pre-FEED Full/outline specifications (subsea, vessel, topsidesl Design basis
Main drawings
PFD and P&IDs
Verification weight, heat, mass, power, utilities etc
Initial RAM CAPEX&OPEX
Project economics
O&Mphilosophy Local content options
Products&Trading
Safety review Offloading availability FEEDscope
merciai negotiations
Explore and select commercial model(s) Commercial and financialCPsand milestones
Negotiate agreements(MOU, LOI, HoA,F10) with terms & conditions Define vessel reservation and allocation terms & conditions Financing
Stakeholder meetings
Support activities
!benefit
PlanLocal presence Publications and info sessions
- FEED
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ft
Figure 4 LNG P generic approach and parallel projects offer great project development benefits
The development line, as shown in the figure, resembles with many other oil&gas projects. However there are a number of distinct features that make the project development ofan LNG Producer different and some are described hereafter.
s Data-room evaluation
Evety project starts by evaluating the existing work that has been done. In order to support the clients with this initial assessment ofthe LNG Producer for a potential project, a data-room has been established. Here, all the design, engineering, testing and verification studies are stored and are available for detailed review. Making this wealth of information available to potential clients is essential to draft the first design basis for a new project.
Fast track development
At the start of a project there is a wealth of information already available from the design work by FLEX and contractors as well as parallel projects. By utilizing the existing LNG Producer design and engineering work and the lessons-learnt from parallel projects the development phases can be significantly shorter than comparatively sized oil&gas projects
Low costs for development work until FID
By utilizing the existing design and engineering work the costs for concept, pre-FEED and FEED phases are significantly reduced.
Reliable deliverabi es from early phases
A new oil or gas project that start from scratch will have significant uncertainties for the first deliverables. As FLEX LNG has progressed on several projects well into the development timelines the actual design solutions for new LNGP projects are significantly less uncertain. Or in other words, various parts of the concept for a new project have already been detailed up to a FEED or detail design stage.
More reliable costs figures in early phases
Although a project is in a concept or pre-FEED phase various parts of the concept for a new project have already been Full specifications
Drawings
Detailed EPCICproj ect
plan and schedule Negotiated contraci
O&M plan LLI ordered
Complete RAM,SIL,FSA
studies Dynamic process simulations Model basin tests
detailed up to a FEED or detail design stage. Consequently, the cost estimates are more accurate and require less contingencies than concept studies that really start from scratch.
Generic topsides reduce scope of work
A large part of the topsides is the generic part. For most new projects this part is more than sufficiently engineered for the first project phases and this reduces the scope of work significantly.
Although every project has elements of the illustrated project development timeline, there are numerous differences between every client and every project.
Some example project cases
A few examples are provided that illustrate some of the key design changes that have been done to accommodate the LNG Producer for the specific project.
Case I: African project
Some key project specifics:Permit development Condensate handling High air temperatures
Throughout 2008 FLEX LNG worked with the project partners to develop the approval application, which was successfully received from the authorities by the end of 2008 without important changes to the LNGP design. Various solutions were evaluated how to handle the condensate. Initially the condensate was to be exported through the turret and a riser to a nearby FPSO. Later in the project, interface and schedule issues supported a condensate handling and storage solution on the LNG Producer. Based on the portfolio of projects all the hulls on order by FLEX were enlarged for this purpose.
The high air temperatures and also temperature fluctuations were identified as an uncertain factor for the performance of the gas turbines. In order to provide maximum output and a stable process performance an air chilling system was adopted and incorporated on the inlets.
Case 2: Asian project
Some key project specifics: Onshore gas Shallow water Permit development
For this project the feedgas is onshore and will be transported by pipeline to an offshore location. A cost and feasibility study for the pipeline was therefore conducted. The offshore area is rather shallow and becomes only gradually deeper. Deeper water is preferred for the design of the turret-buoy and mooring system. However, moving to deeper water will imply a longer pipeline for this case. Detailed studies were thus conducted to demonstrate the feasibility of the internal disconnectable turret system for shallow water. Permitting for the site and the pipeline shall be developed with the government and local bodies and a permitting plan is thus prepared. Changes to the LNGP are not foreseen because of this.
Case 3: Non-benign environment with rich and varying feedgas compositions
Some key project specifics: Harsh environment High HHC content
Varying feedgas compositions Permit development
The harsh environment puts additional design requirements on the vessel and topsides in terms of strengthening, protection, material selection, insulation, utilities. The key changes were identified in an early phase and incorporated in the design. In order to maintain sufficient offloading availability several tandem offloading concepts were evaluated for integration on the LNG Producer.
The feedgas was rich on higher hydrocarbons. After some initial process evaluations it was concluded to develop a separate LPG extraction, stabilization system. Likewise the hull design was changed to include an 1MO Type A LPG storage tank as well as a stern offloading system for this product.
As the feedgas is provided from different sources there are significant differences in the composition. The field specific topsides are therefore designed for these inlet variations and the suitability of the nitrogen expansion cycle system was confirmed.
Case 4: Deep water application
Some key project specifics: Deep water
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Although the waterdepth itself does not affect the LNG Producer it does affect the risers, the mooring and the interfaces between subsea and topsides. Currently, APL is developing an STP solution for the Cascade Chinook FPSO using free-standing hybrid riser technology for a waterdepth of 2600 meter. This feasibility demonstration provided the support to start developing the STP application on the LNG Producer for this deepwater application as well.
Case 5: High CO2 content
Some key project specifics: High CO2 in feedgas
A range of discovered fields have been less interesting to oil&gas companies because of their high CO2 content. Developing proper technical solutions for the LNGP to extract, reinject CO2 and sequestrate enables the LNG Producer to monetize these gas fields. Various concepts have been designed for bulk CO2 removal and which can be incorporated as an additional module on the field specific topsides.
Conclusions
FLEX LNG has been working for more than 3 years to develop the LNG Producer. The enormous amount of design and engineering that has been conducted has provided a robust generic design that is easily adapted to the majority of the potential projects. The latter is demonstrated by a variety of projects that are under development.
All the design and engineering that have been done were essential to develop an optimal generic design, from which every project start. Starting a new project with a basic design that has a range of systems already designed beyond the FEED stage provides clients with cost efficient and quick development timelines. Moreover the utilization of previous design work and the lessons-learnt from parallel projects give better accuracy and reliability in early project phases and provide thus full comfort to proceed developing floating LNG projects.
The LNG Producer, currently being designed for various projects and clients, will add a new branch to the LNG industry. And this development will show that floating LNG projects can be developed quickly, cost efficient, for small to medium fields and for difficult fields and locations.
