Liquefied Gas Carrier
LNG carrier









The carriage of liquefied gases in bulk -Where do the products come from ?


The liquefied natural gas (LNG) industry in the United States and other countries was developed to link huge gas reserves in geographically remote parts of the world with regions in need of more natural gas. For example, Japan and Korea import LNG to meet almost all their natural gas needs, and half of Spain's natural gas demand is met through the importing of LNG.





Most liquefied gases are hydrocarbons and the key property that makes hydrocarbons the world’s primary energy source – combustibility – also makes them inherently hazardous. Because these gases are handled in large quantities, it is imperative that all practical steps are taken while carrying through sea transports.

Vessels involved in the LNG trade are generally recognised as integral parts of the overall projects in which they serve. This means that their safety and security feature very prominently in the minds of the LNG sellers and buyers who believe that the vessels also carry their individual reputations. This concern is most evident when the vessels are alongside loading or discharging terminals where any type of incident could reflect adversely on the terminal owner's business.

The carriage of liquefied gases in bulk began in the late 1920s and the earliest ships carried butane and propane in pressure vessels at ambient temperature. The subsequent development refrigeration techniques and, more particularly, materials suitable for containment at low temperature permitted the carriage of cargoes at temperatures below ambient.

In the late 1950s these gases began to be carried commercially in a partially refrigerated state in ships equipped with pressure vessels made with material tolerant of low temperatures. By the mid-1960s fully refrigerated LPG ships were in service carrying cargo at atmospheric pressure; ethylene and LNG ships had also entered service. In the meantime ammonia had become a common cargo, and “chemical” gases such as butadiene also became commercially important.

Liquefied natural gas ship underway
The process of liquefaction ­ changing a gas to a liquid ­ may be achieved in one of three ways:
  • Reducing its temperature by refrigeration at atmospheric pressure.
  • Applying pressure at ambient temperature.
  • A combination of the above.
WHERE DO THE PRODUCTS COME FROM? LNG is produced from natural gas. LPG may be produced either from natural gas or from refining crude oil.

Different forms of liquefied gas cargo require different transport modes, means and storing methods.
Gases and liquids have to be contained in some form. They may be stored into tank containers or flasks, or alternatively be moved without packaging in pipelines and special carriers.





When gas is moved in tanks onboard ships, it is often liquefied by low temperature. This is a highly specialised form of transport requiring not only expensive, purpose built carriers, but also special terminals and handling equipment. There are two forms of gas which are shipped by sea, liquefied natural gas (LNG) and liquefied petroleum gas (LPG). The advantages of cooling gases can be evidenced in the simple arithmetic that liquid gasses can be reduced by about 600%.

Most liquefied gases are hydrocarbons and the key property that makes hydrocarbons the world’s primary energy source – combustibility – also makes them inherently hazardous.

Because these gases are handled in large quantities, it is imperative that all practical steps are taken to minimize leakage ,to limit all sources of ignition and prevent marine pollution.The majority of liquefied gases are clean, non-polluting, products and create no danger to the marine environment. If however certain liquefied gases spill on to the sea you should be aware that they may:
  • create large quantities of vapour ­ sea water rapidly vapourises the liquid gas- which may cause a fire or explosion or a health hazard.
  • generate toxic vapours, which can drift, sometimes over a considerable distance.
  • dissolve in seawater and cause local pollution


The cargo Data Sheets will give information on pollution, if any Pollution is most likely to occur during cargo or bunkering operations:
  1. if the operation is not correctly monitored
  2. if the cargo hose or loading arm connections are not properly made
  3. when disconnecting cargo lines that have not been drained.
  4. if moorings are not checked and excessive strain is placed on the cargo connections or the ship "breaks out" of the berth.
  5. if cargo equipment is not properly maintained
Carrying low temperatures cargoes

When carrying low temperature, or cryogenic, cargoes this introduces other potential hazards like frosbite. If exposed to severe cold flesh will become frozen.
At first the skin becomes red (but turns subsequently white); the affected area is painless but is hard to the touch. If left untreated the flesh will die and may become gangrenous.

Wherever you are at risk of contact with very cold liquids always wear sufficient clothing to protect your entire body ­ in cargo areas full PPE (personal protective equipment) may be required.




Treatment:
  1. remove any clothing that may restrict circulation to the frozen area of the skin
  2. immediately immerse the affected area in a water bath having a temperature of between 40ºC and 46ºC until it has thawed
  3. do not `massage' the affected area
  4. obtain urgent medical assistance


Caution ! AVOID SKIN CONTACT WITH UNINSULATED PIPES AND VALVES IN THE CARGO AREA


Below is our articles on gas carrier types and safety procedure.

Type of gas carriers - variation in the design, construction and operation

Gas cargo containment systems - primary barrier (the cargo tank),secondary barrier, thermal insulation and more



Related Information:

  1. Liquefied gas carrier safety training


  2. Risk of LNG vapour cloud


  3. vaporized gas (BVG) management system for carrying LNG cargo


  4. Volatile nature of liquefied gases





External links :

  1. International maritime organization












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The content published in this website are for general reference only. We have endeavoured to make the information as accurate as possible but cannot take responsibility for any errors. For latest information please visit www.imo.org . Any suggestions, please Contact us !



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