Pre-treatment process to remove carbon dioxide (CO2) and hydrogen sulfide (H2S) from natural gas using amine solvents. Critical to prevent freezing and corrosion during liquefaction.
APCI (Air Products and Chemicals, Inc.)
Major LNG technology licensor. Developer of the C3MR (Propane Pre-cooled Mixed Refrigerant) liquefaction process, used in ~50% of global LNG capacity.
Autoignition Temperature
Minimum temperature at which a fuel will spontaneously ignite without an external ignition source. For methane: 538°C (1000°F).
B
BAHX (Brazed Aluminum Heat Exchanger)
Compact, high-efficiency heat exchanger made of aluminum alloy, used extensively in LNG liquefaction. Also called "cold box." Vulnerable to mercury contamination (liquid metal embrittlement).
Baseload LNG
Large-scale, continuous LNG production typically from dedicated liquefaction facilities (4-8 MTPA per train), as opposed to peak-shaving or small-scale operations.
Bcf (Billion Cubic Feet)
Unit of natural gas volume. 1 Bcf ≈ 28.3 million cubic meters. Often used as Bcf/d (per day) for flow rates.
Bcm (Billion Cubic Meters)
Unit of natural gas volume. 1 bcm ≈ 35.3 Bcf. Common in European and Asian reporting.
Bio-LNG
LNG produced from renewable sources such as biogas from landfills, agricultural waste, or wastewater treatment. Chemically identical to fossil LNG but with near-zero or negative carbon lifecycle emissions.
BOG (Boil-Off Gas)
Natural gas vapor that evaporates from LNG due to heat ingress, even in insulated tanks. Typical rates: 0.1-0.15% per day for modern carriers, 0.03-0.05% for land storage. Managed via ship propulsion, reliquefaction, or flaring.
Bunkering
The process of supplying fuel to ships. "LNG bunkering" refers to refueling vessels with LNG as marine fuel, increasingly adopted due to IMO 2020 sulfur regulations.
C
C3MR (Propane Pre-cooled Mixed Refrigerant)
The most widely used liquefaction technology (Air Products/APCI). Uses propane for pre-cooling to -40°C, then a mixed refrigerant (nitrogen, methane, ethane, propane) to cool to -162°C. Achieves ~90% thermodynamic efficiency.
Cascade Cycle
Liquefaction process using three separate refrigerant loops (propane → ethylene → methane). Highest thermodynamic efficiency (~92%) but more complex equipment. Developed by ConocoPhillips.
CCS (Carbon Capture and Storage)
Technology to capture CO2 emissions from liquefaction facilities and store them underground. QatarEnergy's North Field expansion will capture 11 MTPA of CO2 by 2035.
CCGT (Combined-Cycle Gas Turbine)
Power generation technology using both gas and steam turbines to achieve ~60% efficiency. When fueled by natural gas, emits ~40% less CO2 than coal-fired plants.
CNG (Compressed Natural Gas)
Natural gas compressed to 200-250 bar at ambient temperature. Volume reduction ~200:1 (vs. LNG's 600:1). Used for vehicle fuel and short-distance transport.
Cryogenic
Pertaining to very low temperatures, typically below -150°C (-238°F). LNG operations require cryogenic-grade materials that remain ductile at -162°C.
D
Dehydration
Process to remove water vapor from natural gas to prevent ice and hydrate formation in cryogenic equipment. Target: <0.1 ppm moisture (dew point < -100°C).
DMR (Dual Mixed Refrigerant)
Shell's liquefaction technology using two mixed refrigerant cycles. More compact than C3MR but slightly lower efficiency. Suitable for mid-scale trains (3-5 MTPA).
DWT (Deadweight Tonnage)
Total weight a ship can safely carry (cargo, fuel, crew, provisions). LNG Q-Max carriers: ~100,000 DWT.
E
EPC (Engineering, Procurement, Construction)
Contracting model where a single contractor delivers a complete facility. Major LNG EPC contractors: Bechtel, TechnipFMC, Chiyoda, Saipem.
ESD (Emergency Shutdown System)
Automated safety system to isolate and shut down LNG equipment in case of leak detection, fire, or seismic event.
F
FID (Final Investment Decision)
The point at which a project sponsor commits capital to proceed with construction. A critical milestone in LNG project development.
FLNG (Floating LNG)
Offshore liquefaction facility on a ship-based platform. Example: Shell's Prelude FLNG (488m long, 3.6 MTPA capacity). Enables monetization of remote offshore gas fields.
FOB (Free On Board)
Pricing term where buyer takes ownership when LNG is loaded onto the ship. Buyer bears transportation cost and risk.
FSRU (Floating Storage and Regasification Unit)
Ship-based regasification terminal. Receives LNG carriers, stores LNG, vaporizes it, and delivers gas to shore via pipeline. Faster and cheaper to deploy than land-based terminals (6-24 months vs. 3-5 years).
G
GCU (Gas Combustion Unit)
Equipment to safely burn excess boil-off gas when it cannot be used as fuel or reliquefied. Avoided when possible due to emissions and energy waste.
GIIGNL (International Group of LNG Importers)
Industry association representing LNG importers worldwide. Publishes annual trade statistics and technical reports.
GTL (Gas-to-Liquids)
Technology to convert natural gas into liquid fuels (diesel, naphtha) via Fischer-Tropsch synthesis. Not LNG, but an alternative monetization pathway for stranded gas.
GWP (Global Warming Potential)
Metric comparing greenhouse gas potency relative to CO2. Methane: GWP-20 = 84, GWP-100 = 28. Critical for assessing methane leakage impacts.
H
Henry Hub
Natural gas pricing benchmark in Erath, Louisiana (USA). Used as reference price for North American gas and many LNG contracts. Symbol: HH. Unit: $/MMBtu.
HHV (Higher Heating Value)
Total energy content of a fuel including condensation heat of water vapor. For LNG: ~55 MJ/kg. Contrast with LHV (Lower Heating Value: ~50 MJ/kg).
Hydrate
Ice-like crystalline compound formed when water molecules cage around gas molecules at low temperature and/or high pressure. Can block pipelines and equipment. Prevented by dehydration or methanol injection.
I
IEA (International Energy Agency)
Intergovernmental organization providing energy data, analysis, and policy recommendations. Publishes the Global LNG Capacity Tracker.
IGC Code (International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk)
International Maritime Organization (IMO) regulations governing design, construction, and operation of LNG carriers.
IGU (International Gas Union)
Global gas industry association. Publishes the triennial World Gas Conference and annual World LNG Report—key data sources for the industry.
J
JKM (Japan-Korea Marker)
Spot LNG price benchmark for Northeast Asia. Reflects supply-demand dynamics in the world's largest LNG import region. Published by Platts, Argus, and others.
Joule-Thomson Effect
Thermodynamic principle where gas cools upon expansion through a valve or porous plug. Exploited in liquefaction refrigeration cycles.
L
LDAR (Leak Detection and Repair)
Systematic program to identify and fix methane leaks. Critical for reducing greenhouse gas emissions and maintaining LNG's climate advantage over coal.
LFL (Lower Flammable Limit)
Minimum concentration of fuel in air to support combustion. For methane: 5% by volume. Below this, mixture is too lean to ignite.
LNG (Liquefied Natural Gas)
Natural gas cooled to -162°C (-260°F) at atmospheric pressure, reducing volume by 600:1. Primarily methane (85-95%) with ethane, propane, and nitrogen.
LNG Carrier
Specialized cryogenic tanker for transporting LNG. Types: Q-Max (266,000 m³), Q-Flex (210,000 m³), conventional (125,000-175,000 m³). Tank designs: Moss (spherical) or Membrane (prismatic).
M
MCHE (Main Cryogenic Heat Exchanger)
The primary brazed aluminum heat exchanger in a liquefaction train. Can be 60+ meters tall and weigh over 1,000 tonnes.
Membrane Tank
LNG carrier tank design using thin stainless steel or Invar membrane supported by insulation. Prismatic shape maximizes cargo volume. Contrast with Moss spherical tanks.
Methane Slip
Unburned methane released from engines or industrial processes. Also refers to fugitive methane emissions across the LNG value chain. Critical for lifecycle greenhouse gas assessment.
MMBtu (Million British Thermal Units)
Common energy unit in LNG trade. 1 MMBtu ≈ 1.055 GJ. Henry Hub prices quoted in $/MMBtu. 1 tonne LNG ≈ 52 MMBtu.
Moss Tank
Spherical LNG carrier tank design (Moss-Rosenberg system). Free-standing aluminum alloy spheres insulated with polyurethane foam. More expensive but highly reliable. Used on ~25% of global LNG fleet.
MTPA (Million Tonnes Per Annum)
Standard unit for LNG facility capacity. 1 MTPA ≈ 48 bcm of natural gas ≈ 1.3 Bcf/d. Global liquefaction capacity (2026): ~520 MTPA.
N
NFPA 59A
U.S. National Fire Protection Association standard governing LNG production, storage, and handling. Sets thermal radiation and vapor dispersion exclusion zones.
NGL (Natural Gas Liquids)
Heavier hydrocarbons extracted from natural gas during pre-treatment: ethane, propane, butane, pentane. Valuable co-products sold separately from LNG.
Nickel Steel (9% Ni)
Steel alloy containing 9% nickel, maintaining ductility at cryogenic temperatures. Used for LNG storage tank inner walls.
O
OGMP 2.0 (Oil and Gas Methane Partnership)
UN Environment Programme initiative for transparent methane emissions reporting and reduction. Targets <0.2% methane intensity by 2030.
ORV (Open Rack Vaporizer)
Regasification equipment using seawater as heat source to vaporize LNG. Simple and low-cost but can cause local seawater cooling (ecological concern in some regions).
P
Peak Shaving
Storage of LNG during low-demand periods for vaporization during peak winter demand. Helps utilities balance seasonal gas consumption.
Pool Fire
Fire that occurs when spilled LNG is ignited at the release point. Large but relatively contained. Less dangerous than a delayed vapor cloud explosion (VCE).
PRICO (LINDE Process)
Single Mixed Refrigerant (SMR) liquefaction technology. Simple design suited for small-scale plants (<3 MTPA) and offshore FLNG.
Q
Q-Flex
LNG carrier size: 210,000-217,000 m³ capacity. Developed by Qatar for Suez Canal transit optimization.
Q-Max
Largest LNG carrier class: 266,000 m³ capacity. Developed by Qatar. Membrane tank design. Can carry energy equivalent of 159 million cubic meters of natural gas.
R
Regasification
Process of warming LNG to convert it back into gaseous natural gas for pipeline distribution. Achieved via seawater vaporizers, ambient air vaporizers, or submerged combustion vaporizers.
Reliquefaction
Process of compressing and re-cooling boil-off gas (BOG) back into liquid. Used on modern LNG carriers to achieve near-zero BOG emissions.
S
SCV (Submerged Combustion Vaporizer)
Regasification equipment that burns fuel gas to create hot water for vaporizing LNG. Used when seawater is too cold or environmentally restricted.
SMR (Single Mixed Refrigerant)
Simplest liquefaction technology using one mixed refrigerant circuit (nitrogen-heavy blend). Lower efficiency than C3MR but fewer equipment pieces. Suitable for small-scale and offshore use.
SPA (Sale and Purchase Agreement)
Long-term contract for LNG supply, typically 15-25 years. Specifies pricing formula (oil-indexed or hub-indexed), volume commitments, and destination flexibility.
Spot Market
Short-term LNG trading (single cargoes or <4-year contracts). Priced via JKM (Asia), TTF (Europe), or Henry Hub + liquefaction fee (USA). Growing share of global trade (now ~40%, up from 10% in 2010).
STP (Standard Temperature and Pressure)
Reference conditions for gas volume: 15°C (59°F) and 1 atmosphere. Used to normalize gas volumes for comparison.
T
Tcf (Trillion Cubic Feet)
Large unit of natural gas volume. 1 Tcf ≈ 28.3 bcm. Often used for reserves estimates.
Tolling Agreement
Contract where the facility owner processes (liquefies) customer-supplied gas for a fee ($/tonne or $/MMBtu). Customer retains title to the LNG. Common in U.S. Gulf Coast projects.
Train
A single liquefaction production line, from pre-treatment through refrigeration to storage. Modern baseload trains: 4-8 MTPA capacity. A facility may have multiple trains (e.g., Sabine Pass has 6 trains totaling 30 MTPA).
TTF (Title Transfer Facility)
European natural gas pricing benchmark (Netherlands virtual trading hub). Increasingly used for LNG contracts replacing oil-indexed pricing. Symbol: TTF. Unit: €/MWh.
U
UFL (Upper Flammable Limit)
Maximum concentration of fuel in air to support combustion. For methane: 15% by volume. Above this, mixture is too rich to ignite (insufficient oxygen).
V
VCE (Vapor Cloud Explosion)
Explosion resulting from delayed ignition of a dispersed LNG vapor cloud in a confined or semi-confined space. Most serious LNG hazard scenario. Mitigated via vapor fences, water curtains, and dispersion modeling.
Virtual Pipeline
Concept of transporting small-scale LNG via truck or small vessels to off-grid locations, providing natural gas without physical pipelines.
W
Wobbe Index
Measure of gas interchangeability, defined as heating value divided by square root of specific gravity. Critical for ensuring imported LNG matches pipeline gas specifications for burners and turbines.