Chilling natural gas to minus 162 shrinks it six hundredfold
Natural gas is bulky and hard to keep from leaking, which is why oil drillers long treated it as an unwanted byproduct. Cool it to about minus 162 °C, though, and it condenses into a clear liquid occupying roughly one six-hundredth of the space, small enough to cross oceans in tankers.
Liquefied natural gas is mostly methane with a little ethane. Before chilling, plants strip out water, carbon dioxide, hydrogen sulfide, mercury and heavier hydrocarbons that would freeze or damage equipment. The liquid is then held in double-walled insulated tanks at close to normal atmospheric pressure. It has no colour or smell, is not toxic and does not corrode, though it is flammable once it vaporises and can cause freezing burns or suffocation. Per litre it packs about 2.4 times the energy of compressed natural gas, but only about 60 percent of diesel's.
The science stretches back centuries. Robert Boyle linked gas pressure and volume in the seventeenth century, and Karol Olszewski first liquefied methane in 1886. In 1915 Godfrey Cabot patented a storage tank built like a Thermos flask, an insulated inner vessel inside an outer one. In 1937 Lee Twomey patented large-scale liquefaction using the Joule-Thomson effect, in which a gas cools as it expands repeatedly through a narrow opening. His aim was to bank gas for winter cold snaps.
The first commercial plant opened in Cleveland in 1940 for exactly that purpose, but in October 1944 a tank ruptured and the resulting fire killed 130 people, stalling the industry for years. Better alloys and insulation revived it. In 1959 a converted wartime Liberty ship, the Methane Pioneer, carried a cargo from the US Gulf Coast to Britain, and in 1964 the Methane Princess became the first tanker built for the trade. A decade of Phillips Petroleum work produced a cascade process using propane, ethylene and methane in turn, first used in Alaska in 1969.
America built terminals on its East Coast expecting to import gas, then fracking flipped the flow. Its first export shipment left in early 2016, and by 2023 the country was the world's biggest exporter, shipping 4.3 trillion cubic feet that year.
Source: Liquefied natural gas
