Quote from chief_editor on October 18, 2023, 8:29 pm

Floating liquefied natural gas (FLNG) is an innovative technology that allows for the extraction, processing, liquefaction, and storage of natural gas at sea. FLNG vessels are essentially giant floating factories that sit directly above offshore gas fields, enabling the monetization of reserves that were previously unavailable for development.

FLNG provides access to offshore stranded gas fields that lack the infrastructure for pipeline transportation. By placing the liquefaction facilities directly at the offshore gas field, FLNG avoids the costly and environmentally contentious process of building long-distance pipelines to onshore facilities. The FLNG facility produces liquefied natural gas (LNG) - natural gas that has been cooled to -160°C and condensed to 1/600th of its original volume - which can then be offloaded to LNG carriers for transport to markets around the world.

The Development of FLNG Technology

The development of FLNG technology has been driven by a desire to unlock stranded offshore gas fields that are either too remote, too small, or too deep to justify the construction of pipelines and onshore liquefaction infrastructure. With FLNG, gas fields can be developed faster and on a much smaller scale than was previously possible.

While onshore LNG plants have been around since the 1960s, it wasn’t until the 1990s that the first concepts for floating liquefaction began to emerge. The technological challenge of accommodating massive liquefaction facilities on a floating platform was significant. It required major innovations in areas like maritime engineering, materials technology, mooring systems, and the cryogenic handling of liquids at sea.

The world’s first FLNG project was the Prelude facility, located offshore northwest Australia and operated by Shell. Construction began in 2012 and operations commenced in 2019. Measuring 488 meters long and weighing over 200,000 tonnes, the Prelude FLNG is the largest floating facility ever constructed. Its success proved that FLNG technology was both feasible and commercially viable, paving the way for more projects to follow.

How an FLNG Facility Works

An FLNG facility is essentially a floating liquefaction plant and LNG storage tank all in one. It contains all the major processing equipment needed to take natural gas from the reservoir and convert it into liquefied form for export. The main components and operations onboard an FLNG facility are:

Gas Extraction and Processing Deck This deck sits at the waterline and connects directly to subsea gas wells via flexible risers and flowlines. It receives the untreated reservoir fluid, separates out the gas, and treats it to specification by removing impurities like CO2, H2S and mercury.

Liquefaction Deck After processing, the lean gas moves to the liquefaction deck where it goes through a multi-stage cooling process to condense it into a liquid. Using refrigerants like propane and mixed refrigerant systems, cryogenic heat exchangers cool the gas down to -160°C, at which point it condenses into a liquid that takes up 1/600th the volume of gaseous natural gas. This allows it to be transported efficiently by ship.

LNG Storage Tanks The liquefied gas is stored in on-board insulated tanks. Depending on the facility, there are typically two to six LNG storage tanks holding 150,000 - 180,000 cubic meters of LNG each. The LNG is held at approximately -163°C to keep it in liquid form before it gets pumped onto LNG carriers.

Offloading System FLNG facilities are equipped with offshore offloading systems to transfer LNG to carriers. These use cryogenic transfer arms and specialist loading hoses that can safely move LNG between the vessels while floating at sea.

Utilities and Accommodation Like any large industrial facility, FLNG vessels also contain power generation, water supply, air compression, and living quarters for the crew. The accommodation block is typically near the back of the facility, farthest from the gas processing areas.

Innovative Technologies Enabling FLNG

While the core process of liquefaction is well proven and understood, adapting the technology to a floating platform required some innovative engineering. Key innovations that have enabled FLNG include:

• Improved lightweight materials - FLNG facilities utilize advanced high-strength steels, composites, and aluminum alloys to reduce weight while still maintaining structural integrity in a marine environment. This improves floatability/stability.
• Dynamic positioning systems - These thruster systems allow the FLNG facility to actively stay on station above the gas field without anchors. Dynamic positioning gives flexibility to quickly disconnect and reconnect to wells.
• Disconnectable turret mooring - A disconnectable turret chained to the seabed allows the FLNG vessel to weathervane freely around it. Flexible risers and umbilicals are routed through the turret to the subsea wells.
• Cryogenic materials - Special materials like 9% nickel steel allows liquefaction equipment to withstand temperatures down to -163°C without becoming brittle and fracture.
• Sloshing containment - Baffle systems inside LNG tanks prevent excessive movement of liquid that could generate forces sufficient to damage the tank structure.
• Floating LNG offloading - Cryogenic loading arms and specialist LNG carrier vessels enable liquid transfer in open sea conditions.

Advantages of FLNG

FLNG offers a number of advantages over the conventional approach of piping gas onshore for liquefaction and export. The main drivers for FLNG projects are:

Speedier Development Timelines With no need for long-distance pipelines to shore, FLNG facilities can be deployed faster above gas fields. This greatly reduces lead times compared to onshore plants which need pipelines built first. For a stranded reserve, FLNG could cut development time from over a decade down to just 5-6 years.

Access to Stranded Reserves FLNG unlocks gas fields trapped in offshore locations where pipelines are impractical. Global estimates suggest up to 20% of gas reserves are stranded - FLNG gives a way to produce these reserves.

Reduced Costs Eliminating hundreds of kilometers of pipelines represents major cost savings. Exact savings depend on the field’s distance offshore, but FLNG capital expenditure is generally 10-50% less than pipelines to shore depending on project specifics. Operating costs are also less as there is no pipeline to maintain.

Flexibility FLNG facilities are not fixed permanantly like onshore plants. Once a gas field becomes depleted, the FLNG can disconnect and move onto another field. This extends the asset life and improves project economics.

Reduced Local Impact With facilities contained far offshore, FLNG avoids community disturbances, visual impacts, and land use conflicts with coastal onshore facilities. It also eliminates risks of gas leaks and right-of-way constraints from shore-crossing pipelines.

Lower CO2 Emissions No long transmission pipelines to shore translates into significantly less embodied carbon emissions in steel pipe manufacture. Exact GHG savings vary by project, but FLNG emits 21-37% less CO2e over the liquefaction facility life cycle.

Challenges for FLNG Projects

While having considerable advantages, FLNG facilities also come with some technological and commercial challenges, including:

Harsh Offshore Environment Open ocean conditions impose enormous forces including waves, wind, and currents. Ensuring structural integrity and connectivity to wells in severe storms is a persistent engineering challenge. Materials selection and intelligent mooring arrangements are critical.

Larger Upfront Capital Expenditure Although FLNG saves on pipelines, the upfront capex of converting a gas carrier into an FLNG factory is massive - up to $5-10 billion. This requires strong project economics and off-take agreements to underpin financing.

Untested Reliability As floating facilities housing volatile cryogenic liquids, reliability questions remain until an FLNG vessel demonstrates a strong uptime track record. The technology is still considered in its early stages.

Inflexible LNG Offtake Buyers often prefer flexibility around cargo delivery timing, which is constrained with FLNGs at a fixed offshore location rather than pooled onshore liquefaction capacity.

Future Outlook for FLNG

The global FLNG market has gained significant momentum since the Prelude project proved the concept. Analysts predict the FLNG industry will grow substantially as it unlocks new gas reserves and reduces development costs. Wood Mackenzie forecasts global FLNG capacity will reach 26 million tonnes per annum by 2030.

Key companies active in the FLNG sector include Shell, Petronas, Exmar, Golar LNG, Black & Veatch, TechnipFMC, and Samsung Heavy Industries. These firms are pushing the boundaries to make FLNG economically viable for a wider range of stranded field developments.

New technological improvements like standardization, modularization, all-electric drives, and optimized hull designs will also enhance FLNG productivity and competitiveness. Combining FLNG with floating production storage and offloading (FPSO) vessels will open even more offshore prospects to development.

With global energy demand continuing to rise, FLNG promises to be an increasingly vital tool for cleanly unlocking natural gas that was previously stranded and turning it into a fungible, marketable commodity. The technology epitomizes innovation in the natural gas industry and will facilitate an important transition fuel as the world gradually decarbonizes its energy system.