The Coral Sul FLNG: sustainability and innovation

Cost-effective, environmentally sensitive, and efficient: There are many benefits to accessing liquified natural gas under the sea from a floating liquified natural gas facility. These facilities extract natural gas from an offshore field and then process it onsite so it can be easily transported. Unlike traditional fields on land, this relatively new way of extracting natural gas means there's less need for long pipelines, previously remote fields can be accessed and the products can get to the market faster.

Currently there are two FLNG facilities in the world, but the third one, Eni's Coral Sul, is on its way:

• Petronas PFLNG SATU
• Shell Prelude FLNG
• Eni Coral Sul

The world's first operating FLNG, Petronas' PFLNG SATU, started production in 2016. The 388 meter-long facility, nearly the size of four football fields, is located off the coast of Malaysia. It was designed by engineers in France and Malasysia and built in South Korea. Designed to last for 20 years, this FLNG has enabled the development of remote fields that were previously inaccessible. The cost of construction is believed to be around $10 billion and the facility has a processing capacity of 1.2 million tonnes per annum (mtpa). The facility can be moved between fields to access natural gas in hard-to-reach locations as well. Petronas implemented several innovations in this facility to address the known challenges with an FLNG plant, including a dual row cargo containment system that protects the low-temperature storage tanks located in the hull from movement that could impact the operation of gas processing equipment.

The Shell Prelude is located 125 miles off the coast of Australia and began production from three wells in 2018. It shipped its first cargo in 2019. The 488 meter-long plant was built in South Korea and has the capacity to produce at least 5.3 million tonnes of liquids per year. That includes 3.6 mtpa of LNG, 1.3 mtpa of condensate, and 0.4 mtpa of liquefied petroleum gas. Condensate and LPG are two secondary products of LNG production. Shell says its storage tanks can hold the same amount of liquid as 175 Olympic-sized swimming pools. The goal is for the facility to be in operation for 20 to 25 years. However, it is estimated to have cost between $12 and 17 billion. Last year, an electrical trip shut down the Prelude's LNG production between February 2020 and January 2021. Though technical issues frequently arise in complicated processing facilities, the shutdown underscored the fragility and complexity of the infrastructure underpinning this FLNG.

Eni's first FLNG, the Coral Sul will be located off the coast of Mozambique and is scheduled to begin production in 2022. When it's up and running, it is expected to deliver 3.4 mtpa of LNG entirely to bp. The vessel is 432 meters long and weighs around 200,000 tonnes, with space for an eight-story living module, accommodating up to 350 people. Like its FLNG predecessors, the Eni FLNG vessel was constructed in South Korea with Samsung Heavy Industries. This will be the world's deepest FLNG facility with wells drilled nearly 2,000 meters deep. Six wells in total will flow into the liquification unit.

One major challenge in the development of the FLNG was the weather in the Indian Ocean where the Coral Sul is located. The area is prone to cyclones and design engineers needed to take that into consideration, building a facility that could withstand challenging weather conditions. To ensure that Coral Sul FLNG can operate safely even in the most extreme weather conditions, the project team, with the support of the most prestigious marine and meteorological research institutes, carried out several simulations in tanks and wind tunnels. It is expected that the plant will be able to stay offshore for 25 years without dry-docking.

The Coral Sul will include cutting edge technology, including four turbo-compression systems to refrigerate the product and generate power for onboard equipment.

For gas liquification, the Coral-Sul deploys an efficient APCI Dual Mixed Refrigerant solution, radically different from Petronas' nitrogen expansion based one which is tailored to smaller capacities. To safeguard against refrigerant compressor failure, the Coral Sul contains two parallel 50% capacity strings so if one of the two compressors fails, the other circuit will still provide half the output (versus none if the whole system shuts down). The floating plant will also have boil-off gas and booster compressors to capture and re-liquefy excess boil-off gas that escapes the cryogenic tanks as vapor. This addition improves the overall efficiency of conversion to LNG.

Another ground-breaking feature of the Eni Coral Sul plant is in the construction of the hull. The Samsung Heavy Industries (SHI) team assembled the 132,000-ton hull with over 2,000 building-block structures. SHI grouped the fundamental blocks into larger subassemblies and continued building until the hull was complete. This approach simplified the manufacturing of the hull by standardising the blocks and drastically reduced construction time. The Coral Sul will be equipped with digital oil field and maintenance technologies, utilizing advanced data analytics and key performance indicators to enable optimal plant performance. Due to the cold storage temperature, an automated well control will dictate the production rate to maximize the vessel's available refrigeration capacity.

Sustainability was a major consideration throughout the design and development of the Coral Sul, according to Eni's Coral South Project Director Juan Carlos Coral. For example, vapor recovery improves the liquification process's sustainability by increasing the conversion percentage of gaseous natural gas to a liquid. “We have ambitious plans to reduce our carbon emissions and that goal was at the heart of the development of our first FLNG facility," said Coral.

“Natural gas is projected to increase its share in the world's overall energy mix. It is a key transitional fuel based on its comparatively lower emissions with respect to other fossil fuels. These global trends are reflected in our carbon neutrality plans to get to net zero emissions by 2050, leveraging, among other factors, an increase to 90% of natural gas in the production mix with an expansion of our LNG portfolio." Other elements that were included to reduce the carbon footprint:

• Aero-derivative gas turbines
• Variable-speed electric engines
• Low-loss, high-voltage electric transformers
• Maximized system waste heat recovery (WHR) efficiency
• Boiler exhaust WHR
• High-efficiency gas treatment

These features aim to reduce the amount of input energy the gas-to-liquid conversion requires, and minimize disruption to the local environment. The higher efficiency reduces the CO2 and NOx emitted into the atmosphere. This efficiency-driven design is expected to place the Coral Sul below the industry benchmark in terms of energy consumption. There was also a significant effort made to protect Eni's Coral Sul against LNG spills. “Before construction, we undertook detailed cryogenic spill protection studies to reduce the potential of cryogenic liquid spills. This translated into both the installation of selected materials and coatings and the development of fit-for-purpose drainage facilities," said Coral.

Though located offshore, the Coral Sul project will have a positive impact on the communities nearby. This is part of the Sustainable Development Goals to which we have made part of our business model. “This initiative will train more than 800 Mozambicans for the specialized plant operations. Eni is also adding social, economic, and health care support in the spirit of creating a sustainably better community as a result of its work," said Coral. Local suppliers are key to our success and Eni Rovuma Basin has a web portal available in Portuguese, where they can apply for this status.

To date, more than 600 Mozambican suppliers have been registered in the company's database, and about 240 are now eligible to work on Eni projects. More than that, Eni believes that training is crucial to develop skills for the next generation. In 2019, Eni and Standard Bank together launched an enterprise development programme which has promoted business links and opportunities for over 100 Mozambican SMEs. Eni has also supported a women's entrepreneurship program, the Lioness of Africa, which has reached nearly 600 Mozambican entrepreneurs. Eni's involvement in training is long-standing and since 2012, we have been involved with vocational training initiatives, like the 200 Programme, which aims to train 200 talented and skilled Mozambican graduates in Economics, Health Sciences, Biological Sciences, Engineering, Chemistry, Information Technology and Law.

FLNG is a transformative way to unlock natural gas from previously unreachable locations. The technical and commercial scale of the projects is substantial, but it can profoundly impact both the global market to alleviate supply risk and the local market to influence and grow a local economy. Massive projects like the Shell Prelude, Petronas PFLNG SATU, and Eni Coral Sul must also take steps to protect the local environment, by integrating sustainable technologies on the FLNG. Continuous technological improvement will play an essential role in shaping the future of this sector. Leveraging the lessons learned from this project, Eni is uniquely positioned to shape the execution strategy of future FLNG projects starting from early phases.