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Basic Liquefaction Process

What is LNG?

Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport.

It takes up about 1/600th the volume of natural gas in the gaseous state (at standard conditions for temperature and pressure).

It is odourless, colourless, non-toxic and non-corrosive.

The feed gas generally undergoes pre-treatment involving removal of certain components, such as acid gases, water, and heavy hydrocarbons, which would cause difficulty in the liquefaction process.

The natural gas is then condensed into a liquid at close to atmospheric pressure by cooling it to approximately −162 °C (−260 °F); maximum transport pressure is set at around 25 kPa (4 psi).

How is LNG created?

The process begins with the pre-treatment of a feedstock of natural gas entering the system to remove impurities such as H2S, CO2, H2O, mercury and higher-chained hydrocarbons. Feedstock gas then enters the liquefaction unit where it is cooled to between -145 °C and -163 °C.

Although the type or number of heating cycles and/or refrigerants used may vary based on the technology, the basic process involves passing the gas through aluminium heat exchangers (cold box) and exposure to a compressed refrigerant. As the refrigerant is vaporised, the heat transfer causes the gas in the passes to cool.

The LNG is then stored in a specialised insulated tank at atmospheric pressure ready to be transported to its final destination.

How is LNG transported and stored?

Most domestic LNG is transported by land via truck/trailer designed for cryogenic temperatures. These units consist of an internal steel or aluminium compartment and an external carbon or steel compartment with a vacuum system in between to reduce the amount of heat transfer.
Once on site, the LNG must be stored in vacuum insulated or flat bottom storage tanks.

How is LNG changed back into gas?

When ready for distribution, the LNG enters a regasification facility where it is pumped into a vaporiser and heated back into gaseous form.
The gas then enters the pipeline distribution system and is delivered to the end-user.