Natural gas liquefaction follows thermodynamic phase transition laws. When the temperature is below the critical point (methane -82.6℃), the gas phase can be transformed into the liquid phase by increasing pressure or decreasing temperature.
Under normal pressure, liquefaction requires cooling to -162℃, while at 4.5 MPa pressure, it only requires cooling to -84℃. This process requires overcoming the kinetic energy of gas molecules, which is achieved by the compressor performing work and heat exchangers removing heat, thus reducing internal energy.
The product formed after liquefaction is called liquefied natural gas (LNG), whose main component is methane. LNG has a volume 625 times smaller than the same mass of natural gas, making it easier to store and transport. LNG has a flash point of approximately 650℃ and an explosive limit range of 4.7%~15%, making its production and use relatively safe.