Liquified Natural Gas (LNG)
A product of natural gas which consists primarily of methane. Its properties are those of liquid methane, slightly modified by minor constituents. One property which differentiates liquefied natural gas (LNG) from liquefied petroleum gas (LPG) is the low critical temperature, about −100°F (−73°C). This means that natural gas cannot be liquefied at ordinary temperatures simply by increasing the pressure, as is the case with LPG; instead, natural gas must be cooled to cryogenictemperatures to be liquefied and must be well insulated to be held in the liquid state. See also Liquefaction of gases; Liquefied petroleum gas (LPG).
LNG offers an energy density comparable to petrol and diesel fuels and produces less pollution, but its relatively high cost of production and the need to store it in expensive cryogenic tanks have prevented its widespread use in commercial applications.
Conditions required to condense natural gas depend on its precise composition, the market that it will be sold to and the process being used, but typically involve temperatures between −120 and −170 degrees Celsius (pure methane liquefies at −161.6 °C) and pressures of between 101 and 6000 kPa (14.7 and 870 lbf/in² [approx 1-60 atm]). High pressure natural gas that is condensed is then reduced in pressure for storage and shipping.
The density of LNG is roughly 0.41 to 0.5 kg/L, depending on temperature, pressure and composition. In comparison water has a density of 1.0 kg/L.