NavArch Simple Sharing #1 FLNG Containment Types

The words Liquefied natural gas (LNG) have been increasing lately. LNG is not a new "thing" for the floating structure industry - as it has existed for a while. Methane Pioneer, the first LNG ship, was built in 1958 and was converted from a cargo carrier into a liquid gas carrier [1,2,3]. However, the development of Floating Liquefied Natural Gas (FLNG) could be categorised as new compared to other floating structures like Floating production storage and offloading (FPSO). Currently, there are a few FLNG in operation that are, including Hilli Episeyo FLNG, Fortuna FLNG, Petronas PFLNG Satu, Petronas PFLNG 2, Coral South FLNG and Prelude FLNG [4]

So, what makes the FLNG special now?

According to studentenergy.org [5], the demand for LNG is increasing due to consumers' desire for cleaner fuels, especially in Asia. Allied Market Research also stated, "The growth of the FLNG market will be accelerated by rising demand for clean fuel technologies and a growing focus on a sustainable energy mix. Rapid depletion of fossil fuels, combined with ongoing efforts to reduce carbon emissions, will help businesses thrive.?" [5].

FLNG Containment Types?

Cargo containment is one of the essential elements in designing the FLNG due to the LNG gas behaviour. This is because the liquid state of the gases is at -162°C, and a simple leakage exposed to the hull structure could make it brittle and result in a material fracture. Currently, there are four options for the FLNG containment:

Option 1: Utilising Membrane Technology [6]

This is successfully implemented by having an LNG-proof metal thin layer (approx 0.7-1.2mm) surrounded by insulation. However, as the layer is structurally weak, the challenges of maintaining structural strength become a risk. This is because the FLNG will operate in harsh conditions where constant sloshing could eventually deteriorate the membrane.

Option 2: Self-Supporting Type (B) [7]

For this type, the tank is a freestanding structure that is capable of sustaining the LNG as it is designed with a thick plate and carefully stiffened. Unfortunately, this will require high construction expenses. (FYI: the internal structure also utilising Option 1 technology)

Option 3: Moss Tank

A spherical shape with a thick plate. Unfortunately, the spherical shape could not maximise the cargo hold, with at least 50% of the cargo hold area needing to be utilised more. Yet, it is known that Option 3 is the most robust and has a very low susceptibility to damage due to sloshing.

Option 4: Type C

Type C has a concept identical to Moss Tank but was designed to be Cylindrical. Even though it may not utilise the designated cargo hold area, it has a higher volume than Option 3. Typically, the tank will be located entirely within the hull.

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References:

Ref [1] https://www.wartsila.com/encyclopedia/term/lng-tanker

Ref [2] https://greatlakes.bgsu.edu/item/437032

Ref [3] https://higherlogicdownload.s3.amazonaws.com/SNAME/1dcdb863-8881-4263-af8d-530101f64412/UploadedFiles/c3352777fcaa4c4daa8f125c0a7c03e9.pdf

Ref [4] https://www.offshore-technology.com/features/biggest-flng-tankers/?cf-view

Ref [5] https://studentenergy.org/transport/liquefied-natural-gas-lng/#:~:text=The%20demand%20for%20LNG%20is,shutdown%20of%20nuclear%20power%20plants.

Ref [6] https://www.wartsila.com/encyclopedia/term/membrane-type-lng-cargo-containment-system#:~:text=Membrane%20systems%20exploit%20the%20double,and%20thermal%20insulation%20%E2%80%93%20is%20applied.

Ref [7] https://www.ihi.co.jp/offshore/whatisspb_e.htm