liquefied natural gas

Liquefied natural gas is methane and other hydrocarbons cooled to approximately -162 degrees Celsius at atmospheric pressure, reducing volume to roughly 1/600th of the gas state. This phase change allows pipeline-remote gas reserves to reach distant markets by ship without the enormous pressure vessels required to transport compressed gas. The process is capital-intensive but economically justified for fields far from consumption centres or where pipeline infrastructure is impractical.

Liquefaction plants operate through multi-stage refrigeration cycles, typically using propane or ethylene as intermediate coolants before final cooling with methane itself. The inlet gas must be dehydrated and scrubbed of CO2 and hydrogen sulphide; even small concentrations of these substances freeze solid at cryogenic temperatures and block equipment. Processing chains often include demethanizer and deethane units to separate valuable ethane and propane for separate sale, leaving dry methane as the primary LNG product.

Transport and regasification

Specially insulated LNG carriers maintain the liquid state during sea transport, though boil-off gas escapes continuously and is either burned for fuel or reliquefied. Receiving terminals include regasification units that warm the liquid back to gas using seawater or dedicated heat exchangers, returning it to pipeline-compatible form. Some terminals employ open-rack vaporizers (ORV) that spray LNG directly onto aluminum plates cooled by seawater, while others use submerged combustion vaporizers (SCV) that burn boil-off gas to generate steam for heating.

LNG contracts typically specify a liquefaction plant's capacity in million tonnes per annum (mtpa), referring to the annual throughput of feed gas converted to liquid. Large trains (individual liquefaction units) typically operate at 4 to 6 mtpa per train. Spot cargoes trade alongside long-term contracts, and price volatility has increased as shipping flexibility has grown and smaller-scale import terminals have developed.

The business model depends on arbitrage between low-cost feedstock regions (Australia, Qatar, the Russian Arctic, East Africa) and high-price consuming markets (East Asia, Europe). LNG has reshaped global energy markets by reducing the geographic lock-in of pipeline-bound gas and enabling smaller, more flexible supply chains than the infrastructure-heavy onshore trade. However, the capital requirements and long build timescales mean major projects remain financed by governments and state oil companies alongside international consortia.