Fri. Sep 24th, 2021

City gas distribution

Transporting future fuel

#93 Transportation of liquefied natural gas

4 min read

What is LNG?

LNG is a clear, colorless, and non-toxic liquid that forms when natural gas is cooled to -162ºC (-260ºF). The cooling process shrinks the volume of the gas 600 times, making it easier and safer to store and ship. In its liquid state, LNG will not ignite. 

When LNG reaches its destination, it is turned back into a gas at regasification plants. It is then piped to homes, businesses, and industries where it is burnt for heat or to generate electricity. LNG is now also emerging as a cost-competitive and cleaner transport fuel, especially for shipping and heavy-duty road transport.

Natural gas is extracted from fields located predominantly in countries such as Algeria, Norway, Qatar, Russia, Nigeria and the USA. The distance between these countries and their markets means that it is not always possible to transport the natural gas produced via gas pipelines; in this case, the easiest and most economical alternative is to ship it by sea in LNG tankers.

To enable maritime transport, the natural gas is cooled down by means of a refrigerated cycle (compression, condensation, expansion, evaporation) that transforms the gas into a liquid form at -160°C: this is known as Liquefied Natural Gas (LNG). LNG, which is largely composed of methane (85 to 99%), is odorless, colorless, non-toxic, and non-corrosive.

Once it has been liquefied, very large quantities of Liquefied Natural Gas can be stored and transported in LNG tanker ships. The cargo is transported in thermally insulated tanks, specially designed to maintain the natural gas in liquid form at -160°C.

Transportation of LNG

The transportation of liquefied natural gas (LNG) refers to any movement or shipping of natural gas while in its liquid form. The two major methods of transporting LNG are by pipeline and vessel.

Liquefied natural gas flows efficiently through pipelines so is a preferred method of transporting natural gas. Most LNG pipeline infrastructure takes the LNG between liquefaction facilities and storage facilities, from storage facilities to tankers, and from tankers to re-gasification facilities. LNG is much denser than compressed natural gas (CNG). This means that much higher amounts of gas are able to be transported for the same volume flow. The downside is that LNG pipelines are difficult and costly to construct.

As LNG requires a temperature of -160°C (-260°F) to remain in its liquid form, significant insulation must be incorporated into LNG pipelines in order to maintain this low temperature and ensure no re-gasification occurs. This normally includes a combination of mechanical insulation, for example glass foam and a vacuum layer. This complex insulation system makes LNG pipelines significantly more difficult and expensive to manufacture than standard natural gas pipelines.

The majority of worldwide LNG exports take place at an intercontinental level, meaning that shipping LNG across the ocean is often required. This is done with the use of an LNG vessel or LNG ship, which transports large quantities of LNG between export and import terminals. Several types of LNG vessels exist in the industry today, with the main one being referred to as an LNG tanker.

The main components of an LNG tanker are the boiler and pump rooms, a double hull for added strength, bow thrusters, and the LNG storage tanks themselves.

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