Liquefied Natural Gas （LNG）, whose main component is methane, is recognized as the cleanest fossil energy on earth. It is colorless, odorless, non-toxic and non-corrosive, its volume is about 1/625 of the volume of the same amount of gaseous natural gas, and the mass of liquefied natural gas is only about 45% of the same volume of water.
The manufacturing process is to firstly purify the natural gas produced in the gas field, after a series of ultra-low temperature liquefaction, it is transported by LNG ships. The combustion of liquefied natural gas has very little air pollution, and the heat released is large, so liquefied natural gas is a relatively advanced energy source.
LNG is natural gas that is compressed and cooled to its condensing point （-161.5 ℃） temperature and becomes liquid. Usually, liquefied natural gas is stored in a low-temperature storage tank at -161.5 degrees Celsius and about 0.1MPa. Its main component is methane, which is transported by special boat or tank truck and regasified when used. Since the 1970s, the world 's liquefied natural gas production and trade volume have increased rapidly. In 2005, LNG international trade volume reached 188.81 billion cubic meters. The largest exporter was Indonesia, which exported 31.46 billion cubic meters; the largest importer was Japan 76.32 billion cubic meters. [ 1].
Natural gas refers to combustible gas contained in the formation, mainly a mixture of low molecular alkanes, which can be divided into dry gas natural gas and wet natural gas. The dry gas composition is mainly methane. In addition to a large amount of methane, wet natural gas also contains More ethane, propane and butane.
Liquefied natural gas （Liquefied Natural Gas） is mainly composed of methane, and a small amount of ethane and propane. LNG is colorless, odorless, non-toxic and non-corrosive. Natural gas can be liquefied at normal pressure and around -162 ° C. The volume of liquefied natural gas is about 1/625 of the gaseous volume.
Under normal pressure, the density of LNG is about 430-470kg / （slightly different due to different components）, the ignition point is about 650 ℃， the calorific value is 52MMBtu （1MMBtu = 2.52 × 108cal）, the explosion limit in air （ Volume） is 5% -15%. LNG storage is one of the natural gas storage methods. The LNG storage tank is usually a double-layer metal tank. The inner layer in contact with the LNG is low-temperature steel containing 9% Ni, the outer layer is carbon steel, the middle insulation layer is expanded perlite, and the bottom insulation layer is foam glass.