How natural gas is liquefied

Chilling natural gas to -162 °C shrinks it to one six-hundredth of its volume so ships can carry it.

stations: 5
things upstream: 1
raw source: 1
step from the ground: 1

The short version

Liquefied natural gas is natural gas cooled until it condenses into a liquid at about -162 °C, taking up roughly one six-hundredth of the gas volume. Plants first strip out dust, carbon dioxide, water and heavy hydrocarbons, then run it through successive refrigeration stages. Insulated tanks and ships hold the liquid at that temperature.

Clean the gas

Dust, carbon dioxide, helium, water and heavy hydrocarbons are removed first. Left in, they would freeze and cause upsets in the cold equipment.

Goes in
Natural gas
Pre-cool with propane

In the cascade process, three refrigeration cycles are chained, each sealed off from the gas. Propane circulating in its own loop does the first stage of cooling.
Cool further with ethylene

Ethylene or ethane, also in a closed loop, takes the gas to a lower temperature in the intermediate stage.
Condense with methane

A methane cycle brings the gas down to a liquid. Liquefaction is an energy-intensive process.

-162 °C
Store in insulated tanks

The liquid is kept in tanks with a cold inner shell inside an insulated outer one. Specialized tankers carry it to import terminals, where it is turned back into gas.

End of the lineLiquefied natural gas

Worth repeating

Its energy per liter is about 2.4 times that of compressed natural gas, and 60 percent that of diesel.
The first commercial LNG plant opened in Cleveland, Ohio, in 1940, and a tank failure there in 1944 killed well over a hundred people.