Activated carbon
Carbon processed to create a very large internal surface, often over 1,000 square meters per gram, that holds gas molecules by adsorption.
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- Glossary
Gas storage glossary: CNG, ANG, LNG and hydrogen terms
33 terms used across the guides, each with a short definition and the guide that explains it in depth.
Adsorbed natural gas (ANG)
Natural gas held on the surface of a porous solid inside a tank, typically at 35–50 bar instead of the 200–250 bar used for CNG.
Adsorption
The adhesion of gas molecules to the surface of a solid. It differs from absorption, where molecules enter the bulk of a material.
Bi-fuel vehicle
A vehicle that can run on natural gas or on gasoline from two separate fuel systems, switching between them.
Biomethane
Biogas upgraded to pipeline quality by removing carbon dioxide and impurities, interchangeable with fossil natural gas.
Boil-off
Liquefied gas that evaporates as heat leaks into a cryogenic tank. It is vented, used or reliquefied.
Cascade storage
Banks of high-pressure cylinders at a station, filled to different pressures and drawn in sequence to fast-fill vehicles.
Compressed natural gas (CNG)
Natural gas stored as a gas at high pressure, typically 200–250 bar, in steel or composite cylinders.
Compressibility factor (Z)
The ratio between a real gas volume and the volume the ideal gas law predicts. For methane at 200 bar and 15 °C it is about 0.8.
Cryo-compressed hydrogen
Hydrogen stored cold and under pressure at the same time, combining part of the density of liquid with lower boil-off.
Decompression station
Equipment at the customer end of a virtual pipeline that lets compressed gas down to distribution pressure, heating it to offset the cooling effect.
Diesel gallon equivalent (DGE)
The amount of a fuel with the same energy as one US gallon of diesel.
Embrittlement
Loss of ductility in some metals, especially high-strength steels, exposed to hydrogen.
Fast-fill
Refueling a vehicle in minutes from high-pressure station storage, similar in time to filling with gasoline.
Flaring
Burning gas that cannot be used or transported, common at oil wells far from pipelines.
Gasoline gallon equivalent (GGE)
The amount of a fuel with the same energy as one US gallon of gasoline; for CNG it is 5.66 lb, about 2.57 kg.
Heat of adsorption
Heat released when gas adsorbs onto a surface and absorbed when it leaves; it warms an ANG tank during filling and cools it during use.
Heel
The gas that stays held in an adsorbent when the tank reaches its minimum delivery pressure.
Hydrogen blending
Adding hydrogen to natural gas in a pipeline network, usually at a limited share by volume.
Liquefied natural gas (LNG)
Natural gas cooled to about −162 °C, where it becomes a liquid with roughly 600 times less volume than the gas at room conditions.
LOHC
Liquid organic hydrogen carrier: an oil-like liquid that binds hydrogen chemically and releases it again in a heated reactor.
Metal hydride
A metal or alloy that absorbs hydrogen into its crystal lattice and releases it when heated or depressurized.
Metal-organic framework (MOF)
A crystalline material built from metal nodes and organic linkers, with very high internal surface area for adsorbing gases.
Pressure relief device (PRD)
A safety device on a cylinder that vents gas in a fire, before heat weakens the vessel.
Renewable natural gas (RNG)
Methane from landfills, digesters or wastewater, upgraded for pipeline injection or vehicle use.
Standard cubic meter (scm)
A cubic meter of gas measured at a reference temperature and pressure, used to compare quantities stored at different conditions.
Stranded gas
Gas reserves that are known but too small or too remote to reach a market by pipeline.
Time-fill
Refueling vehicles slowly, typically overnight, directly from a compressor, common at fleet depots.
Tube trailer
A road trailer carrying long horizontal pressure tubes or composite modules, used to deliver compressed gas.
Type I to Type IV cylinders
Pressure vessel classes from all-metal (Type I) through hoop-wrapped and fully wrapped metal liners (II, III) to a polymer liner fully wrapped in composite (IV).
V/V
Volumes of gas, measured at standard conditions, stored per volume of tank. The common figure of merit for ANG; the US DOE target was 180 V/V.
Virtual pipeline
Supplying gas by truck, rail or ship in compressed or liquefied form where no pipeline exists.
Wobbe index
The heating value of a gas divided by the square root of its relative density, used to judge whether two gases burn interchangeably in the same appliance.