CNG carrier

CNG carrier

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Compressed natural gas carrier ships are designed for transportation of natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 under high pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

. CNG carrier technology relies on high pressure, typically over 200 bar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

, to increase the density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 of the gas. Full scale CNG carriers are under development. Whether CNG carriers may find their place in competition with the well established technology of liquefied natural gas by LNG carrier
LNG carrier
An LNG carrier is a tank ship designed for transporting liquefied natural gas . As the LNG market grows rapidly, the fleet of LNG carriers continues to experience tremendous growth.-History:...

s in yet to be demonstrated.

Pressure container technology

Several approaches to the problem of a cost-effective high-pressure containers. The main variables are the material to be used and the geometry of the containers. Standard method of storing non-condensed gases in metal flasks is not cost-effective for high-volume storage at high pressure. (This does not apply to gases such as butane
Butane is a gas with the formula C4H10 that is an alkane with four carbon atoms. The term may refer to any of two structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, butane refers only to the unbranched n-butane isomer; the other one being called "methylpropane" or...

 and propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...

 or their mixtures as in liquefied petroleum gas (LPG). LPG gases liquefy at ambient temperatures under moderate pressure and can be economically stored in steel containers of various sizes.)

New approaches to CNG technology include fiber-reinforced plastic containers and containers in the form of metal tubes of moderate diameter (typically 6" or 168 mm internal diameter). In one approach (Coselle) 17 kilometres (10.6 mi) of tubing is wound on a spindle. Such spindles are stackable and may be connected to achieve the desired capacity.