Natural gas refers to flammable gases found in underground strata, primarily a mixture of low-molecular-weight alkanes. It can be classified into dry natural gas and wet natural gas. Dry natural gas is mainly composed of methane, while wet natural gas, in addition to a large amount of methane, also contains significant amounts of ethane, propane, and butane.
Liquefied natural gas (LNG) is primarily composed of methane, with smaller amounts of ethane and propane. LNG is colorless, odorless, non-toxic, and non-corrosive. Natural gas can be liquefied at atmospheric pressure and around -162°C. The volume of LNG is approximately 1/625 of its gaseous state.
At atmospheric pressure, the density of LNG is approximately 430-470 kg/m³ (slightly varying depending on the composition), its ignition point is approximately 650°C, its calorific value is 52 MMBtu (1 MMBtu = 2.52 × 10⁸ cal), and its explosive limits (by volume) in air are 5%-15%. LNG storage is one method of natural gas storage. LNG storage tanks are typically double-walled metal tanks. The inner layer, in contact with LNG, is made of cryogenic steel containing 9% Ni, while the outer layer is made of carbon steel. The intermediate insulation layer is expanded perlite, and the bottom insulation layer is made of foam glass.
In 2022, Qatar became the world's largest LNG exporter with 80 million tons of LNG exports. Global LNG exports reached 399 million tons, a year-on-year increase of 5%.