Liquefied natural gas - Wikipedia, the free encyclopedia
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2004, 19 January, Skikda, Algeria. Explosion at Sonatrach LNG liquefaction facility. 27 killed, 80 injured, three LNG trains destroyed, 2004 production was down 76% for the year. A cold hydrocarbon leak occurred and hydrocarbon gases were drawn into the combustion air for a high-pressure steam boiler. The explosion inside the boiler fire box precipitated a larger explosion of vapors outside the box.
Seaborne LNG transport tankers (including their loading terminals) have not had a major  accident in over 47,000 voyages
 since maritime inception in 1959. There have, however, been several significant incidents with LNG ships, but with only
minor spills. In addition to accidents, terrorism experts are concerned that intentional sabotage could lead to unprecedented releases, resulting in massive fires and other damaging effects. The latter may include detonations (producing large blast waves) and deflagration-to-detonation transition phenomena. As the Department of Energy notes in its December 2004 report (Sandia National Labs, SAND2004-6258), the available testing data on LNG spills are based on releases of very small size in comparison to releases expected from intentional attacks. The Sandia report assumes that a ship's tank with a hole in it (up to several square meters in area) from any cause will drain by gravity while a fire burns outside the ship. This may not be a valid assumption for holes in tanks below the waterline of a vessel, or at the waterline. If the hole is below the waterline, the LNG in contact with water may vaporize violently in a rapid-phase transition, possibly pressurizing the tank and forcing LNG and gas to exit the hole under the water. The Sandia report notes the experimentally observed phenomena of RPT causing extensive damage to a marine structure, and gives a corresponding yield of high explosive for a relatively small LNG spill into water. The extent of damage to an LNG tank from RPT phenomena that could lead to a cascading failure of all tanks on an LNG ship remains to be determined. For a hole at the waterline in the presence of a pool fire, the contact of water with the LNG may also cause RPT at the hole, and might cause a dynamic pressure condition within the holed tank, leading to a higher rate of LNG release than from gravity alone. For a hole above the waterline in the presence of fire, the volume of LNG released from an unvented rigid tank must be replaced by an equal volume of some mass entering the tank. In the context of the Sandia report analysis, the available mass to enter the tank above the waterline consists of one or more of the following components: LNG vapor, air, flame, and combustion products. If the tank is rigid and vented while holed, the same components are presumably present to enter the holed tank. This import of mass and corresponding heat energy might be expected to vaporize the LNG in the tank, and may create the conditions needed for a detonation inside the tank. The recent GAO report of February 2007 (GAO-07-316) surveyed experts who were not unanimous in confirming the findings of the original Sandia report. The expert GAO panel concluded that additional research was needed to understand the potential effects of LNG ship accidents and malevents. The Department of Energy has funded Sandia to continue research, but not all of the topics identified by the GAO study are included in the current Sandia research agenda. While natural gas explosions are common in confined spaces such as houses, claims that outdoor releases of natural gas are at low risk of explosion must consider adjacent structures as enclosed spaces. If an LNG ship release occurs, any buildings, vehicles, or escort vessels close to the release constitute enclosed spaces where natural gas explosions may occur. Despite intense local opposition, the Federal Energy Regulatory Commission has approved a site permit for an LNG terminal in Fall River, Massachusetts in a densely populated harbor area.
P and above ground to suit sites conditions and local safety regulations and requirements. Smaller quantities, 190,000 US gallons (700 m³) and less, are stored in horizontal or vertical, vacuum-jacketed, pressure vessels. These tanks may be at pressures anywhere from less than 5 psig to over 250 psig (35 to 1700 kPa gauge pressure). LNG above-ground tanks are mainly of double-wall, high-nickel steel construction with extremely efficient insulation between the walls. Large tanks are low aspect ratio (height to width) and cylindrical in design with a domed roof. Storage pressures in these tanks are very low, less than 5 psig. Sometimes more expensive frozen-earth, underground storage is used. r e - s t r e s s e d c o n c r e t e b a c k e d u p w i t h s u i t a b l e t h e r m a l i n s u l a t i o n , a r e d e s i g n e d t o b e b o t h u n d e r
LNG storage tank at EG LNG
LNG must be maintained cold (at least below −117 °F or −83 °C) to remain a liquid, independent of pressure. There will inevitably be some degree of boil-off as a result of heat gained from the outside ambient atmosphere. This gas may be returned to storage by recompression and reliquefaction, or used in the liquefaction process. When gas is cooled to -160°C (-260°F), NG becomes liquid and is much more compact-occupying 1/600 of its gas volume. Where long overseas distances are involved, transporting NG in its liquid state is more economical. The LNG industry is set for a large and sustained expansion as improved technology has reduced transportation costs of formerly stranded NG reserves as a liquid to consumer markets.
Transportation and supply is an important aspect of the gas business, since LNG reserves are normally quite distant from consumer markets. LNG has far more mass than oil to transport, and most gas is transported by pipelines. There is a pipeline network in the former USSR, Europe and North America. LNG, when in its gaseous state is rather bulky. Gas travels much faster than oil though a high-pressure pipeline can transmit only about a fifth of the amount of energy per day. As well as
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