Natural gas (methane) is in a gaseous state at normal temperatures and pressures. Liquefied natural gas (LNG) is natural gas that has been converted from a gas to a liquid by cooling the gas below the temperature at which it condenses into liquid. The condensation temperature for natural gas is about –260°F (-162°C). Liquefaction of natural gas reduces the volume of the gas by a factor of about 610. This allows the gas to be stored in a smaller vessel than is required for natural gas in the gaseous state. Natural gas is liquefied for multiple reasons:
- To transport the LNG via tanker on the ocean so that it can be moved long distances from producing regions to consuming regions
- To transport the LNG via tanker truck on land where gas pipeline transport is not available
- To store LNG in above-ground tanks for future regasification and use
LNG is often used for peaking storage on gas distribution systems. In this case gas is taken directly from the gas distribution system, cooled, stored as LNG in tanks, and then reheated (also called vaporized) when it is returned to the distribution system. LNG may also be produced at one location and then trucked to storage or used to keep distribution feeders in service during maintenance using specialized tanker trucks that are capable of storing the LNG, reheating it, and then connecting to a distribution pipe.
Because large volumes of LNG can be moved across long distances where pipelines are not feasible, LNG transported by ships makes it possible for gas markets to access natural gas reserves that are located throughout the world. As of 2019, world trade in LNG was 354.7 million tonnes (17,274 Bcf/489 Bcm).
In the following graphic, the BLUE lines represent LNG trade flows worldwide:
The LNG delivery chain for long-distance transport by ship consists of gas production, gas liquefaction and processing, shipping, and regasification. After the gas is produced, it is shipped by pipeline to a gas liquefaction facility that cools the gas to convert it to liquid. The facility also performs any necessary processing. After liquefaction, the LNG is pumped into tankers and transported across the ocean to the consuming country. There the tanker pumps the LNG into tanks where it is stored until needed. The LNG is subsequently regasified by heating and can then be transported by pipeline to the distribution system. After regasification, the natural gas has properties similar to other gas in the pipeline system.