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.
The process of liquefaction changing a gas to a liquid may be achieved in one of three ways:
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:
The cargo Data Sheets will give information on pollution, if any Pollution is most likely to occur during cargo or bunkering operations:
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.
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
When a gas is stored as a liquid, whether under pressure or refrigeration, it will vaporise when released to the atmosphere, taking heat from its surroundings in so doing. Depending upon the liquid spilled, the spill size and whether the spill is on land or water, the rate of vaporisation and the temperature and density of the ensuing vapour cloud will vary......
The natural BOG is sent to the main boilers by low duty compressor (L/D compressor) through the low duty heater and the flow rate is controlled by L/D compressor speed & inlet guide vane (IGV). If natural BOG does not meet boiler demand, the forcing vaporizer will generate forcing BOG and add it to natural BOG for full speed range of ship. .....
Liquefied natural gas (LNG) compresses to a small fraction of its original volume (approximately 1/600) under liquefaction. With the amount of flammable material that LNG contains, it has the potential to be an extremely dangerous chemical, if handled improperly. The liquefaction of natural gas raised the possibility of its transportation to many destinations. .....
Gas carriers range in capacity from the small pressurised tankers of between 500 and 6,000 m3 for shipment of propane, butane and the chemical gases at ambient temperature up to the fully insulated or refrigerated seagoing tankers of over 100,000 m3 capacity for the transport of LNG and LPG. Between those two distinct types is a third tanker type – semipressurised gas carrier. .....
The most severe accident that may realistically occur to a loaded LNG tanker is the breach of one or more storage tanks, with consequent discharge of liquefied natural gas outboard. No accidents leading to loss of cargo have occurred over the history of maritime liquefied natural gas transportation......
Project “in-service” or “first-gas” dates are important when it comes to developing a gas field. The quicker an explorer can develop his field and bring on his gas production the quicker he can start monetizing his gas.....
An explorer having mid to small size gas reserves (8TCF and less) that are located in remote locations must have access to a pipeline transportation system. If not, their gas is stranded. ....
Compressed Natural Gas (CNG) has been developed as a shipping concept, relying on the high pressure containment technology used in conventional pressure vessel CNG storage and in pipeline systems to provide a form of concentrated gas storage which can be fitted onboard ships. ....
A number of studies have focused on the increase in cargo capacity that could be obtained from changing to dual fuel diesel electric (DFDE) propulsion. When comparing the engine room size of the conventional steam LNGC with the DFDE LNGC, it would be possible to move the engine room bulkhead further aft when using DFDE propulsion. .....
LNG carriers in service are fitted with independent cargo tanks and with membrane tanks. LNG carriers are generally specialised ships transporting LNG at its atmospheric pressure boiling point of approximately -162 degree C, depending on the cargo grade.....
A cargo containment system is the total arrangement for containing cargo including, where fitted: (1) A primary barrier (the cargo tank), (2) Secondary barrier (if fitted), (3) Associated thermal insulation, (4) Any intervening spaces, and (5) Adjacent structure, if necessary, for the support of these elements .....
LNG operating instructions - various important terms .....
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Gas Carriers transporting bulk liquefied gases in trans-ocean services!