Liquefied ethylene gas (LEG) carriers are a type of

gas carrier A gas carrier, gas tanker, LPG carrier, or LPG tanker is a ship designed to transport Liquefied petroleum gas, LPG, LNG, CNG, or liquefied chemical gases in Bulk liquids, bulk. Gases are kept refrigerated onboard the ships to enable safe carriag ...

, a ship designed to transport

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

at sea. Most LEG ships are considered small compared to other gas carriers (typically ) although there are larger LEG ships that have the hybrid capability of carrying liquid natural gas (LNG) and/or

liquefied petroleum gas Liquefied petroleum gas, also referred to as liquid petroleum gas (LPG or LP gas), is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, Butane, ''n''-butane and isobutane. It can also contain some ...

(LPG) as well.

History

Some of the first LEG carriers were built in the 1960s. These include the 1964 ship ''Pythagore'' in France and the 1965 Japanese ship ''Ethlene Maru No 1''.

Gas carriage

LEG carriers are build with a cargo containment system to handle ethylene with a boiling point of . Ethylene is transported at sea for industrial purposes as it is one of the main feedstocks for the

petrochemical industry file:Jampilen Petrochemical Co. 02.jpg, 300px, Jampilen Petrochemical co., Asaluyeh, Iran The petrochemical industry is concerned with the production and trade of petrochemicals. A major part is constituted by the plastics industry, plastics (poly ...

. The low temperature requires fully refrigerated ships with the cargo at atmospheric pressure or semi-pressurised/fully refrigerated (semi-ref) ships with pressure vessel cargo tanks. Semi-refrigerated LEG carriers use special alloyed steels to allow the carriage of ethylene at -104°C. Tanks must be kept in clean and well maintained condition as product purity is important in carriage onboard. Cargo operations on these ships are carried out with a view to avoiding impurities affecting the cargo and in ensuring cargoes are carried at atmospheric pressure.

Design and equipment

The design and construction of LEG carriers operating internationally is regulated by the

International Maritime Organization The International Maritime Organization (IMO; ; ) is a List of specialized agencies of the United Nations, specialized agency of the United Nations responsible for regulating maritime transport. The IMO was established following agreement at a ...

through the

International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk The International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk, often referred and abbreviated as the IGC Code, is the International Maritime Organization (IMO) standard concerning the cargo carriage of liquefi ...

. LEG ships are fitted with a re-liquefaction plant for ethylene. Some ships also have the capability for

ethane Ethane ( , ) is a naturally occurring Organic compound, organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is List of purification methods ...

, and LPG, as well as for various petrochemical cargoes. A pressure swing adsorption (PSA) plant is sometimes used to separate some gases from a mixture of gases under pressure on LEG carriers. Most ships utilise a number of compressors onboard. Some new LEG carriers are being built with dual fuel capability, including the use of LNG alongside existing marine gas oil (MGO) to reduce

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

emissions.

References

{{ModernMerchantShipTypes Ship types Tankers