energy bridge the world’s first lng offshore solution

© Gastech 2005

ENERGY BRIDGETM

The world’s first

LNG Offshore solution

By

Patrick Janssens

Chief Technical Officer

EXMAR

ENERGY BRIDGETM

© Gastech 2005 Janssens 2

ENERGY BRIDGETM The world’s first LNG Offshore solution

1. Introduction As an alternative to the expansion of onshore LNG import terminals Exmar has in cooperation with Excelerate Energy and DSME developed the “Energy BridgeTM”, an innovative concept and design allowing an LNG vessel to regasify the LNG on board and discharge the high pressure gas directly into the consumer grid system, through a dedicated mooring arrangement and sub sea high pressure pipeline directly or indirectly connected to a natural gas distribution network, thereby bypassing the need for an onshore LNG import terminal. This new concept has several advantages:

1) Permitting: The regulatory hurdles for Energy BridgeTM are much lower than with land-based terminals, especially considering the security concerns that have arisen post September 11th.

2) Flexibility: The system is comparatively easy to move to meet the demand at varying locations. This will allow local markets to develop where the cost of onshore terminals would be prohibitive.

The Development of the concept started in early 2001. The first vessels were contracted in May 2002 with Daewoo Shipbuilding and Marine Engineering (DSME) in Korea, a leading shipyard in the construction of the latest generation of LNG carriers. At the time this paper is written one Energy BridgeTM vessel, named EXCELSIOR, has been delivered following successful completion of its sea and gas trials, and a further two are under construction. Delivery of the second vessel, named EXCELLENCE, follows in April 2005. Delivery of the third vessel, to be named EXCELERATE, is foreseen in October 2006. The Excellence prior undocking in March 2004

Typical Energy Bridge field arrangement

ENERGY BRIDGETM


The first offshore mooring buoy will be installed in the Gulf of Mexico and is expected to be operational early in 2005. As such the Energy BridgeTM deepwater port will be the first offshore LNG regasification terminal in the world and is scheduled to commence supplying natural gas to the U.S. market during the first quarter of 2005. The paper will briefly discuss the development of the Energy BridgeTM vessel from its conceptual stage to the development of the design and execution of the project.

2. Basic requirements Starting from a conceptual idea it was important to define the fundamental needs of the project. These basic requirements were summarized as follows:

- Ability to discharge Natural Gas (NG) offshore into a NG distribution network

- Regasification capacity to be at least 500MM standard ft³ per day (approx. 13.4MM Nm³ per day)

- Provide a system with a maximum of flexibility to widen the field of possible applications: o Ability to work in different environmental conditions. o Use of alternative heat sources. o Allow discharge of NG at a wide range of discharge pressures (35 bar up to 100 bar) o Adjust to other site specific requirements (NG temperature, environment, …) o Allow discharge of NG at sea or at a dedicated berth ashore.

- Mooring system able to connect, disconnect and operate in a wide range of environment conditions.

- Maintain the ability to operate the vessel as a conventional LNG carrier

- Rely on existing technology as far as possible (“proven design”)

- Maintain a very high safety level

- No venting of NG under normal operations

Based on these requirements it was necessary in a first stage to develop a conceptual design for the main installations on board to determine the feasibility of such concept. In order to maintain the maximum flexibility with conventional terminals the design was based on a standard 138,000 m³ LNG carrier. Starting from this design several systems needed to be added or modified to suit the basic requirements for the project.

As a starting point following issues needed to be considered:

- Offshore mooring system o Choice of mooring system o Design of a gas transfer system o Structural Design

- Regasification plant o Conceptual lay-out o Choice of main components

- Conceptual safety issues

- Impact on the conventional LNG carrier design o Partial filling during discharge at sea o Manoeuvrability and positioning o Auxiliary power requirements o Heating sources o Other requirements

ENERGY BRIDGETM


Arrangement of STL equipment

Heave compensator

Traction winch

Blast relief panels

Flexible jumper

Rope guide

Swivel handling arm

Buoy locking device

Swivel and connector assembly

Ventilation duct

3. The Offshore Mooring System 3.1. STL Mooring System – Conceptual layout The LNGRV will be moored on a Submerged Turret Mooring and Offloading system developed by Advanced Production and Loading (APL) from Norway. This system has an extensive track record on crude oil shuttle tankers in the North Sea. The basis of the STL system is a buoy moored to the seabed. The buoy is pulled into and secured in a mating cone in the bottom of the vessel and thus connecting the mooring system. Internal in the buoy is the turret with connection to the mooring and riser systems. When the STL Buoy is connected the vessel can freely weather vane without the aid of propulsion. Gas is transferred from the regasification plant to the buoy through a flexible jumper, a swivel and a connector all located in the forward STL compartment. When not connected the STL Buoy is floating in an idle submerged position at a designed water depth. This depth may be between 25 and 40 meters with a pickup line to the surface, ready for a new connection. Key features include the ability to connect in sea states up to 5-6 m significant wave height (Hs). The system is furthermore designed to allow the vessel to stay connected in sea states with waves up to 11 m (Hs), corresponding to the 100 year storm for the sites presently under consideration.

The STL buoy in the Gulf of Mexico is installed in a water depth of approx 80 m. Verification of mooring systems through ocean basin tests have verified the feasibility of the STL mooring systems for water depths in excess of 40m. Mooring system analyses have demonstrated the suitability of the STL mooring system for water depths as low as 20 m.

Arrangement of STL Mooring system

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3.2. Swivel and Connector Although the transfer of gas at high pressures is not uncommon in offshore applications (e.g. for gas re-injection on FPSO’s) a specific swivel stack with a hydraulically locking connector and swivel handling arm were newly designed to address the specific needs for this application. A prototype swivel was manufactured and extensively tested to validate the design. The swivel has a duplicated active sealing system with permanent monitoring to detect any possible leakage. The connector has a triple passive sealing system which can be tested prior start of each discharge. A utility swivel is provided for monitoring of the pressure in the sub sea riser and providing control over the valves on the STL buoy and at the PLEM located on the seabed. Special consideration was given to allow disconnecting the system to disconnect even in case of power failure. 3.3. Model testing

In order to validate the behaviour and forces induced by the mooring system extensive model testing has been carried out at the Marintek institute in Trondheim, Norway.

The model tests provided the necessary information on ship motions and loads on the mooring system and the ship structure in the moored condition.

Model testing at MARINTEK, Norway

Swivel handling arm with swivel & connector

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3.4. Structural Design of the STL compartment A detailed Finite Element model was made of the forward part of the vessel in order to confirm the stresses and the fatigue life of this area. The assessment has shown that the design of the STL compartment was not critical for fatigue point of view with a design fatigue life more than 40 years, taking into account 20 % of the ship life spent on buoy.

Notwithstanding all equipment in the STL compartment is designed to be explosion-proof, an analysis was carried out to determine the potential explosion overpressure in the STL compartment in a worst case of a gas leakage followed by an explosion. As a result of this study blast relief panels were provided on the top of the compartment opening at an overpressure of 0.1 bar gauge and the STL compartment has been designed for a maximum pressure of 3.5 bar gauge.

FEM model of fore body, incl. fine mesh of STL compartment Actual STL compartment during erection in dry-dock

Visualization of the simulated worst case gas cloud

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4. The Regasification Plant 4.1. Conceptual layout LNG/NG side: LNG is supplied to the regasification plant through dedicated feed pumps installed in the ships cargo tanks. The LNG is fed to a suction drum and from there distributed to the different regasification trains. Each regasification train consists of a high pressure LNG pump and an LNG vaporizer. From the LNG vaporizers the NG is fed into a common discharge line fitted with a gas metering unit, with a pressure control valve (to maintain the supercritical pressure in the vaporizers). It is then fed either to a subsea pipeline or to a dedicated high pressure ship side manifold which is located at either side of the ship. Heating water side: The primary heating source for the vaporizers is sea water. The sea water is fed from the heating water/ballast pumps, located in the ship’s engine room, through the heating water booster pumps located in a pump room in the ships forward area, from there fed to the LNG vaporizers and finally to an overboard discharge located in the forward area of the ship. Steam heaters are also provided in the forward pump room which allow, depending on the prevailing environmental conditions or regulatory restrictions, additional heating of the sea water before sending it to the vaporizers, or circulation of the heating water in a fully enclosed system thus avoiding entirely the use of sea water. Steam is in this case fed from the ship’s main boilers located in the engine room.

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Schematic Drawing of Regasification

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4.2. Selection of Main Components 4.2.1. Feed Pumps

The feed pumps are retractable type submerged LNG pumps located in a pump well of the pump tower mast within the cargo tanks. In total 3 units of 620 m³/h capacity each are provided. The feed pumps are located in cargo tanks 2, 3, & 4. This type of pumps is commonly used as emergency pumps in membrane type LNG carriers and as main pumps in land based storage tanks. Maintenance on these pumps can be performed without emptying or gas freeing the corresponding cargo tank.

Arrangement drawing of LNG feed pump

Installation of LNG feed pump on Excelsior

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4.2.2. High Pressure LNG pumps Six (6) high pressure LNG pumps are provided, each with a design capacity of 205 m³/h and a head of 2,370 m, allowing a nominal production for each train of 100 MM scf³/d with a discharge pressure op to 100 bar gauge. The pumps are derived from the submerged type, multi stage centrifugal pumps typically used on land based regasification plants. Particular attention had to be paid to the environment on board of the ship. In this respect 2 main concerns had to be addressed: - Whereas land based plants operate in static condition, on ships the accelerations due to the ships

motions must be considered also. In order to address this issue a guide pin/bearing is provided in the lower part of the pump preventing deflection of the pump stack (see fig. item A). Furthermore the main pump bearing was redesigned (See fig item B).

- Also the idle condition needed to be investigated as the pumps will not be running when the ship is sailing. Ship motions and vibrations could cause hammering damage to the bearing in such condition. In this respect a locking mechanism was developed allowing the pump rotor to be lifted off the bearing when the pumps are not running (see fig. item C).

In addition to the main high pressure pumps 2 smaller high pressure LNG pumps are provided, each with a design capacity of 20 m³/h each, mainly intended for starting up and pressurizing the system. These pumps proved also very useful during commissioning of the system allowing the whole system to be pressurized with N2 during the cool down test.

C

B

A Installation of a high pressure LNG pump on Excelsior Design of high pressure LNG pump

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4.2.3. Vaporizer The regasification plant was designed around a set of shell and tube type vaporizers. This type of vaporizer has been extensively used in land based regasification plants, including some recent receiving terminals (e.g. Dahej in India). The use of shell and tube vaporizers has several important advantages for offshore applications:

- Compact (easy to arrange on deck with minimal impact on the conventional LNG part)

- Simple to operate

- Energy efficient (Possible use of natural heat sources, i.e. use of sea water)

- The process is not affected by ship’s motions or environmental conditions. In the design special attention had to be paid to the particular requirements of the marine environment. Again the accelerations due to the ship motions needed to be considered, both from a mechanical strength point of view as well as from a flow characteristic point of view. Extensive Finite Element calculations were carried out to verify the mechanical integrity of the design. By operating the unit only in supercritical condition any significant impact on the gas flow is avoided. (Note: Above the supercritical pressure a fluid doesn’t change from liquid to gas stage. As a result there is no transition from liquid to vapour condition.) Using sea water as the heating medium also meant that special care had to be paid to the material selection. The SW side of the vaporizers is made of high (>6%) molybdenum super austenitic stainless steel with superior corrosion resistance.

FEM calculations carried out for LNG vaporizers

LNG vaporizer leaving factory

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4.2.4. Metering Unit A metering unit is provided to determine accurately the quantity and quality of the natural gas offloaded. The metering unit consists of a duplicated Ultrasonic type flow meter and a gas chromatograph. This type of metering units is extensively used nowadays in land based installations, including Custody Transfer Systems for cross border natural gas pipelines. The accuracy of the system is not affected by the ships motions and can thus be used under any environmental condition. 4.2.5. High Pressure Manifold As an alternative to discharging vaporized natural gas offshore through the STL buoy a high pressure manifold is provided, located on both sides of the vessel, forward of the conventional manifold. This provides the possibility to discharge pressurized NG at a dedicated berth. 4.3. Validation of the Regasification process In order to validate the process, in particular with respect to the expected shipboard accelerations and to confirm the design capacity of the installation it was decided to perform a full scale test on one vaporizer train. In order to simulate the acceleration on the vessel under extreme weather conditions the complete regasification train was installed on hydraulically controlled motion platform. Full scale testing was concluded in October 2003 in Trussville, Alabama, confirming satisfactory operation of the regasification system.

Arrangement of high pressure manifold

Land based test facility under erection in Trussville

Metering unit on Excelsior

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5. Hazard & Safety At a very early stage of the project development a concept safety evaluation (phase I) was carried out with MARSPEC (Lloyd’s Register of Shipping) with the purpose to evaluate the feasibility of the concept from a safety point of view, and to provide clear guidance during the basic design. In a second phase, throughout the detailed design of the systems, a Hazard Identification Study & Hazardous Operations Study (HAZID & HAZOP) was carried out also with MARSPEC (LRS). In addition to the HAZOP, Fire Explosion Risk Assessments (FERA) were independently carried out by the American Bureau of Shipping (ABS) and MARSPEC (LRS). It was also decided in a very early stage to have the regasification plant fully classed and approved by Bureau Veritas, implying full compliance with the rules and regulations of the classification Society, including the International Gas Code (IGC). It is to be pointed out in this respect that compliance with the class rules is not a strict requirement and not common practice in offshore applications.

6. Manoeuvring and Positioning In order to enable the vessel to pick up the STL mooring buoy it is clear that good manoeuvrability and position keeping is very important, so particular attention was paid in this respect. The Energy BridgeTM vessel is equipped with two bow thrusters and one stern thruster. In addition a Manoeuvring Aids and Positioning System (MAPS) was developed in order to allow the vessel to dynamically approach and position itself over the STL buoy. The system had to take into account the limitations imposed by the use of a steam turbine with a fixed pitch propeller, in particular of the necessity to operate the main turbine above the minimum rpm and to minimise the number of start/stops in order to avoid excessive wear and tear on the turbine gears and bearings. Simulations were performed for different environmental conditions to confirm the controllability and position keeping. The MAPS system has the possibility to use two alternative position reference systems for accurate position keeping. - DGPS A Differential GPS system. A dedicated DGPS receiver with antenna located in the forward

mast of the vessel is provided, allowing accurate absolute positioning (within approx 2 m) of the forward part of the vessel (the STL compartment with the buoy mating cone).

- APRS An Acoustic Position Reference System (APRS). A retractable acoustic transceiver is provided on the vessel. Acoustic transponders are located on the lower girth of the STL buoy. This system provides information on the relative position of the STL buoy to the ship (direction and depth).

Combining the information provided form the DGPS system and the APRS system it is also possible to monitor the buoy position and detect any mooring line failure;

ENERGY BRIDGETM


7. Partial Fillings of Cargo tanks 7.1. Design Basis By its nature the LNGRV is intended for operations in partial fillings condition when being turret-moored on the off-loading site. The cargo containment system is based on the Gaztransport & Technigaz (GTT) membrane type No. 96 (invar membrane and plywood boxes filled with expanded perlite). Given the sensitivity of the membrane type cargo tanks to sloshing detailed analysis was performed in a very early stage of the project in order to confirm the feasibility of partial filling of the cargo tanks. The primary aim of this study was to validate the partial filling conditions at a number of buoy sites under consideration as well as the North Atlantic sailing condition. Emphasis was put on the cargo containment system, the cargo tank supporting structure (inner hull) and the pump tower structure, both from the view of extreme sloshing loads and fatigue.

Schematic drawing of MAPS and APRS systems

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7.2. Cargo containment system Partial fillings studies were carried out by GTT through small-scale tank sloshing model tests and by APL/MARINTEK through station-keeping model tests. Verifications have been carried out by Bureau Veritas through Computational Fluid Dynamics (CFD) sloshing simulations and Finite Element (FEM) fast dynamics computations.

General Methodology of Bureau Veritas Sloshing Assessment

As a result of these evaluations the complete cargo containment system was reinforced by extending the use of standard reinforced insulation boxes over the entire cargo tank (except the flat bottom area). Also the inner hull steel structure was significantly reinforced.

FLOW3D Fluid Flow Animation in Tank N°2 of LNG RV

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7.3. Pump Tower The pump tower tubular structure was verified through Static, Dynamic and Fatigue study for all partial fillings, taking into account hydrodynamic loads obtained in sloshing numerical simulations. As a result of this analysis the pump tower structure was extensively reinforced and the pump tower base support redesigned. In addition the liquid dome and base plate were also reinforced.

8. Other Systems In addition to the arrangements described above several ship systems needed to be reviewed. The main modifications can be summarized as follows. 8.1. Main boiler As mentioned the vessel has the ability to provide the heating water with steam fed from the main boilers. In order to achieve a regasification capacity of 450 MM scf/d the size of the main boilers was maximized for this size of vessel to a steam capacity of 71 ton/h (to be compared with 56 ton/h for the “conventional” vessel).

STANDARD FILLINGS UNLIMITED FILLINGS

Reinforcement of pump tower

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8.2. Auxiliary Power Generation The electrical power demand for the regasification system is significantly higher compared to a conventional vessel so the capacities of the turbine generators and the diesel generator were increased to 2 x 3600 kW, resp. 3700 kW each (from originally 3450 kW each). Furthermore an additional generator was installed. 8.3. Ballast system/heating water system Heating water is supplied from the ballast pumps in the engine room. The vessel has three (3) ballast pumps of increased capacity, 5000 m³/h each. Three (3) heating water booster/circulating pumps are provided in the forward pump room. These pumps are identical to the ballast/ HW supply pumps. Three (3) Steam heaters are located also in the forward pump room allowing to heat up the heating water. A dedicated smaller ballast pump is provided to fill the ballast tanks while the regasification system is in operation.

9. Training A high priority was given to crew training. In order to allow the future operators to get familiarized with the system dynamic simulators were developed for both the regasification system and the MAPS system. Both simulators are PC based and are installed on board of each vessel, as well as in the Exmar’s head office, to maximize the training opportunities. Furthermore the bridge simulator at the Antwerp Nautical Academy was upgraded and now includes a model of the Energy BridgeTM and the mooring site. The vessel is also equipped with a dedicated training room to facilitate training on board the vessel.

10. Sea Trials and Gas trials Sea trials and gas trials of Excelsior have been successfully completed end of 2004. During sea trials extensive testing of the STL equipment and the MAPS system was performed, including the pick up in “real” conditions of a dummy STL buoy. During gas trials full functional testing of the regasification system was carried out, including pressurizing the regasification system and regasification with individual High Pressure pumps at low flow. At the time of writing this paper the vessel is ready for delivery in January 2005 and first discharge at the Energy BridgeTM deepwater port is foreseen for early 2005.

Dynamic simulator for the Regasification System

Annex 1 - ENERGY BRIDGETM – Main Particulars


Main dimensions Length overall approx. 277.0 m Length between perpendiculars approx. 266.0 m Breadth, moulded 43.4 m Depth, moulded 26.0 m Designed draft, moulded (cargo s.g. 0.47) 11.4 m Capacities Cargo tanks (100% at –163°C) approx. 138,000 m3

Maximum cargo intake (98.5% filled) approx. 135,910 m3

Water ballast tanks including peak tanks approx. 51,000 m3 Heavy fuel oil tanks including settling tanks approx. 5,700 m3 Deadweight at design draught approx. 69,500 metric tons Complement (incl. 6 Suez crew) 40 persons Propulsion Main propulsion Marine steam turbine Maximum power (MCR) 36,000 HP @ 88.0 rpm Service output (NCR) 32,400 HP @ 85.0 rpm Speed at NCR 19.3 kn Main Steam boilers 71 ton/h @ 61.5 bar

Auxiliary power generation Turbo Generators (Multi stage steam driven): Three sets of 3,700 kW, 6.6 kV each Diesel Generator One set of 3,650 kW, 6.6 kV Heating Water Supply Heating water supply/ballast pumps Three sets of 5000 m³/h @ 30 mTH each Heating water booster/circulating pumps Three sets of 5000 m³/h @ 30 mTH each Regasification Plant High Pressure LNG pump 6 sets of 205 m³/h @ 2,370 mTH each 2 sets of 20 m³/h @ 2,370 mTH each LNG Vaporizers 6 sets of 100 million standard ft³ per day

Operating Mode Design Capacity Comment SW Heated 500MM scf/d @ 100 bar

(SW temp 14.7°C) With one regasification train and 1 set of heating water pumps standby

690MM scf/d @ 100 bar (SW temp 18.3°C)

Steam Heated mode 450MM scf/d @ 100 bar

ENERGY BRIDGETM


Author’s Biography Patrick Janssens, Chief Technical Officer, Exmar Joined in 1989 the CMB group as naval architect in the technical department. As from 1991, after the take over of the CMB group, joined the Technical Department of Exmar and was over this period in charge of newbuilding of several bulk carriers, LPG carriers and container ships. In December 1999 he was appointed Technical Manager of all shipping activities in the CMB group, i.e. for Bocimar (bulk carriers), Euronav (oil tankers) and Exmar (gas tankers). During this period he was responsible for the construction of 6 VLCC’s, 10 Bulk Carriers, 4 LNG carriers, and as such in charge of the design and development of the Energy BridgeTM Vessels. As from July 2003, after the demerger of Exmar from CMB he became Chief Technical Officer of Exmar, in charge of the Technical Department, including the company’s shipping and offshore activities.

Excelsior on her maiden voyage – 15 January 2005

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TABLE OF CONTENT 1. Introduction _____________________________________________________ 2

2. Basic requirements _______________________________________________ 3

3. The Offshore Mooring System_______________________________________ 4

3.1. STL Mooring System – Conceptual layout __________________________ 4

3.2. Swivel and Connector__________________________________________ 5

3.3. Model testing ________________________________________________ 5

3.4. Structural Design of the STL compartment _________________________ 6

4. The Regasification Plant ___________________________________________ 7

4.1. Conceptual layout_____________________________________________ 7

4.2. Selection of Main Components___________________________________ 8 4.2.1. Feed Pumps _______________________________________________ 8 4.2.2. High Pressure LNG pumps ____________________________________ 9 4.2.3. Vaporizer_________________________________________________ 10 4.2.4. Metering Unit _____________________________________________ 11 4.2.5. High Pressure Manifold______________________________________ 11

4.3. Validation of the Regasification process __________________________ 11

5. Hazard & Safety_________________________________________________ 12

6. Manoeuvring and Positioning ______________________________________ 12

7. Partial Fillings of Cargo tanks ______________________________________ 13

7.1. Design Basis ________________________________________________ 13

7.2. Cargo containment system_____________________________________ 14

7.3. Pump Tower ________________________________________________ 15

8. Other Systems __________________________________________________ 15

8.1. Main boiler _________________________________________________ 15

8.2. Auxiliary Power Generation ____________________________________ 16

8.3. Ballast system/heating water system_____________________________ 16

9. Training _______________________________________________________ 16

10. Sea Trials and Gas trials ________________________________________ 16

energy bridge the world’s first lng offshore solution

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