What Is Liquefied Natural Gas?

Liquefied natural gas (LNG) is natural gas that has been cooled to approximately -162 degrees Celsius (-260 degrees Fahrenheit), the temperature at which it condenses to a liquid at near-atmospheric pressure. In liquid form, the volume of natural gas is reduced to roughly one-sixth of one percent of its gaseous volume, making it practical to store and ship to locations not connected by pipeline. LNG is predominantly methane, with small amounts of ethane, propane, and nitrogen remaining after processing. The energy sector uses LNG to enable international trade in natural gas between producers and consuming markets separated by oceans.

The LNG value chain spans three major stages: liquefaction at the production site, marine transportation in specialized tankers, and regasification at import terminals before delivery to end users through the existing gas grid. Each stage involves substantial infrastructure investment and engineering precision, given the cryogenic temperatures and flammability of the commodity.

Liquefaction Process and Properties

Before liquefaction, raw natural gas from wells must be pretreated to remove impurities that would freeze or interfere with downstream equipment. This includes water, carbon dioxide, hydrogen sulfide, and heavy hydrocarbon components. The treated gas then passes through a refrigeration cycle that progressively lowers its temperature until it crosses the boiling point of methane at the operating pressure. Commercial liquefaction processes use cascade refrigeration cycles, mixed-refrigerant cycles, or expansion-based cycles, with the Air Products and Chemicals C3MR (propane-precooled mixed refrigerant) process accounting for a large share of installed global capacity. The U.S. Energy Information Administration's overview of LNG describes the liquefaction process and the configuration of export terminals. Liquefaction accounts for a significant fraction of the total energy consumed in the LNG chain, driving ongoing research into more efficient thermodynamic cycles and waste-heat recovery.

Storage and Transportation Infrastructure

LNG storage tanks are double-walled, vacuum-insulated vessels designed to hold the liquid at cryogenic temperatures for extended periods with minimal boil-off. Large baseload storage tanks at export and import terminals hold tens of thousands to hundreds of thousands of cubic meters. The boil-off gas that inevitably evaporates is either re-liquefied or used as fuel for the facility. Ocean transport is handled by LNG carriers, ships equipped with cryogenic cargo containment systems. The two principal membrane-type designs, GTT Mark III and NO96, use thin stainless-steel or invar metal linings backed by insulation panels. Moss Rosenberg-type spherical tanks mounted above deck represent an alternative design. As of the early 2020s, LNG carrier fleets number in the hundreds of vessels, and the U.S. Department of Energy tracks the growth of U.S. LNG export capacity, which became the world's largest on an annual basis in 2023.

Regasification and End Use

At import terminals, LNG is pumped from ship tanks to shore storage and then warmed through heat exchangers to convert it back to gas for injection into the pipeline network, a process called regasification or vaporization. Heat sources for regasification include seawater (open-rack vaporizers), submerged combustion vaporizers burning a small fraction of the gas, or ambient air vaporizers. Floating storage and regasification units (FSRUs) allow countries to import LNG without permanent onshore terminal infrastructure, reducing capital costs and deployment time. FSRUs have enabled rapid expansion of LNG imports in markets across Southeast Asia, South America, and Europe. According to IEA reports on global gas markets, LNG trade has grown substantially over the past two decades as new liquefaction capacity in the United States, Australia, and Qatar entered service.

Applications

Liquefied natural gas has applications across a range of energy and industrial sectors, including:

• Power generation at natural-gas-fired combined-cycle plants in markets without pipeline access
• Industrial fuel for manufacturing, chemicals, and refining operations
• Marine fuel as a lower-emission alternative to heavy fuel oil under IMO 2020 sulfur regulations
• Heavy road transport as a fuel for long-haul trucks
• Peak-shaving and gas supply security for utilities managing seasonal demand variation