Alberto Osorio Liebana
Invenergy
Chicago
Energía del Pacífico (EDP) is an LNG-to-power project in El Salvador, where most power generation comes from imported heavy fuel oil (HFO). This $1 billion project, the largest private investment to date in El Salvador, will meet 30% of El Salvador’s energy demand and is scheduled to be operational by end-2021.
EDP seeks to diversify and increase the reliability of El Salvador’s energy mix. Reliable power generation will drive economic growth and contribute to the stability of the region.
The project—being headed by Invenergy and supported by El Salvador-based partners Grupo Calleja, VC Energy de Centroamerica, and Quantum Energy—includes four components:
- Floating storage and regasification unit (FSRU) to store and regasify LNG.
- Subsea pipeline to transport the regasified LNG to the onshore power plant.
- 378-Mw thermal power plant.
- 44-km, (27.3-mile) 230-kv transmission line and associated substations to connect electrical output to the national grid.
In addition to introducing the first LNG-fueled power plant to El Salvador, this project includes the region’s first FSRU. Regulations needed to be formulated and approved for offshore gas storage as well as for transportation to shore. The scope of the transmission network expansion posed another difficulty because rights-of-way negotiations had to be finalized before construction could begin.
Concept development
Initial development concepts included onshore regasification and LNG tanks, a jetty, and an offshore FSRU barge protected by a near-shore cofferdam. Sited close to shore in 17-m water depth and exposed to open ocean swell, these options became very expensive and rendered the project potentially unviable. In the end, the most practical and cost-effective solution was a permanently moored FSRU.
EDP procured the Gallina Moss LNG carrier (LNGC) from Shell and contracted BW LNG to operate the vessel as an FSRU. Gallina Moss has been renamed BW Tatiana and is in lay-up in Singapore. It will be converted to an FSRU this winter and is scheduled to arrive in El Salvador for the EDP project in mid-2021.
The FSRU will be moored on the Pacific coast of El Salvador, orientated at roughly 225° to minimize waves on the starboard bow and to position mooring lines from the stern of the vessel to avoid interfering with pipelines. The exact site was chosen to minimize interference with other port infrastructure, port traffic, and anchorage areas, and place it outside both the nearby terminal exclusion zone for buoy-moored oil imports and the associated marine-terminal operations.
The FSRU will have 137,000 cu m of storage and 280 MMscfd of regasification capacity; four times the throughput needed to operate the power plant at maximum capacity, providing a high level of reliability and redundancy. The FSRU will receive LNG via ship-to-ship (STS) transfer from LNGCs supported and maneuvered alongside the FSRU by SAAM Towage-operated tug boats. LNGCs will be positioned along the starboard side of the FSRU. LNG is transferred between the two moored vessels via midship manifolds using cryogenic hoses. The LNG will be regasified onboard the FSRU and gas delivered to shore from the regas manifold on the FSRU via a riser from a port side porch to a pipeline end termination (PLET) connecting to a 1,750-m subsea pipeline to the onshore power plant.
EDP has signed a 13-year agreement with Shell to supply LNG for the development.
Mooring system
To move forward, the project required an affordable mooring system which could permanently station an FSRU for 20 years in 17-m water depth and operate without interruption. The mooring site is south of the tropical cyclone belt in an area with relatively benign environmental conditions. But the vessel would be exposed to seasonal long-period swell and possible seismic activity with the potential to create tsunamis. Design considered 100-Year wave, wind, and current events and 1,000-Year tsunami events, including sea level variations and current speeds.
Nominal 100-Year conditions include:
- 100-Year significant wave height of 3.3 m with peak periods of 12-18 sec.
- 100-Year wind speeds of 20 m/sec (1-hr mean).
- 100-Year surface currents of 1 m/sec.
CAN Systems AS, Norway, developed and designed the restricted catenary mooring (RCM) system, a refined spread mooring system that comprises a bow mooring system, a mooring restrictor arrangement, and stern hold-back lines. The main feature of the RCM system is a specialized, subsurface connecting plate and restrictor arrangement that keeps mooring lines at the bow and stern close together down to below keel level, eliminating potential interference with the offloading LNGC.
The RCM system consists of the bow mooring system secured by chains affixed to connecting plates arranged from deck-level hangoff with restrictor chains to hold the mooring lines together and away from side-by-side moored LNGCs, avoiding interference during offloading. The holdback lines arranged at the stern have a similar arrangement as the bow mooring lines. The flexible 14-in. export gas risers are routed from a balcony at the side of the ship to the PLET on the seabed where it transitions to the pipeline that carries the gas to shore.
The seabed where the FSRU will be moored is relatively sandy with volcanic boulders, which led to selection of Vryhof’s Stevshark Rex drag embedment anchor for the mooring system. The REX anchor is designed with spread shanks and a geometry that improves installation, penetration, stability, and strength. The RCM mooring system uses 84-mm chain for the lower anchor legs and 100-mm chain in the top chains for additional corrosion allowance in the splash zone (above the restrictor chain). Mooring legs have variable length of 135-235 m to fit within site restrictions. The Vryhof Stevshark Rex anchors vary in weight from 12.5 to 23 tons including extra ballast.
Model testing to confirm the RCM design in 100-Year wind, wave, and current conditions was carried out by Maritime Research Institute Netherlands, which included positioning an LNG carrier alongside the FSRU in STS loading conditions and other scenarios in which any single component in the mooring system could be lost.
Further simulations removed the most loaded line and the second-most loaded line. Results formed the basis for both necessary line tensions with a broken line and FSRU offsets. For these single-component failure scenarios, the criterion for peak loads in the remaining anchor lines and 100-Year extreme condition loads was defined by API RP 2SK, the industry standard for mooring systems. CAN Systems also conducted simulation and modeling to validate mooring performance for tsunami conditions.
The validated mooring arrangement was verified and approved for use on the EDP project by classification society DNV GL.
Moving gas to shore
Royal Boskalis Westminster NV will install EDP’s pipeline under a turnkey contract that includes dredging, installing roughly 1.8-km (1.2-miles) of 24-in. OD line from the onshore power plant to the offshore FSRU, and backfilling over the line, as well as installing the mooring and riser system that connects to the PLET. At the offshore location, Boskalis will preinstall a riser to connect the FSRU to the pipeline, in addition to preinstalling the mooring spread with 11 anchors to permanently moor the FSRU in position. For these activities, Boskalis will deploy a construction support vessel (CSV), a medium-sized trailer suction hopper dredger, a backhoe dredger, and other smaller support vessels.
While most of the work is routine for Boskalis, making the shore approach for EDP is environmentally difficult. El Salvador’s Pacific cliffs are protected, and the location of the onshore power plant means the pipeline delivering gas from the FSRU to the power station would have to run either over or through the cliff where it meets the shore. The negative visual impact created by going over the cliff led to dismissal of that option.
The original plan was to use horizontal directional drilling to bore through the volcanic soil of the cliff, but there was a risk of equipment getting lodged in the hole if the bit encountered a boulder or even having a collapse in the tunnel if drilling lasted longer than expected. The engineering team decided to install the pipeline via an encased tunnel created by microtunneling boring machines instead. Boskalis will assemble the pipeline on shore and pull it through the microtunnel and trench using a winch on the CSV.
The final phase of the offshore component involves connecting the RCM mooring lines and flexible riser to the FSRU. This part of the project will be supervised by BW Offshore Ltd. BW LNG will commission and operate the FSRU.
Power plant
The pipeline will deliver gas from the FSRU to the new 378-Mw power plant being built by Wärtsilä Oyj Abp. This smart power generation plant will provide one-third of El Salvador’s electricity.
The project will also displace older, dirtier, less efficient generation. Today, close to 50% of the 1,600-Mw generation capacity in El Salvador is based on HFO. The new plant will produce 30% less carbon and 99% less sulfur dioxide emissions than HFO and is outfitted with 19 high-efficiency Wärtsilä 50SG engines.
Transmission infrastructure
The deficit in power generation in El Salvador translated into a corresponding deficit in transmission lines, so the EDP project includes adding 44 km (27.3 miles) to the country’s transmission network. The lines will run north through mountainous terrain to Ahuachapán.
A separate underground transmission line will also connect the EDP power station to the nearby Acajutla substation, creating a new loop in the Salvadoran transmission system. This segment of the project will extend transmission across six municipalities, strengthening both the country’s electric grid and the Central American Electrical Interconnection System, which serves Panama, Costa Rica, Honduras, Nicaragua, Guatemala, and El Salvador.
The author
Alberto Osorio Liebana is director of thermal engineering at Invenergy and project director of the Energía del Pacífico (EDP) project under development and construction in Acajutla, El Salvador. Osorio brings more than 15 years’ experience in development of sustainable power generation projects to these roles. He has also been a professor of regulatory framework and quality control in construction in the University of La Salle, Mexico City’s, master’s program in project and construction company management. He holds a BS in civil engineering from the University of Granada, Spain, a BS in civil engineering from the National Autonomous University of Mexico, and an MS in engineering of roads, canals, and ports from the University of Granada, Spain. He is a licensed professional engineer in Spain and Mexico.
