LNG is transported from producing countries in specially-designed double-hulled tankers to prevent leakage or rupture. The double-hull provides increased structural safety, and the insulation allows the ships to act like thermos bottles to keep the LNG cold. The LNG is stored in a special containment system within the inner hull at atmospheric pressure.
Large LNG tankers hold up to approximately 138,000 cubic meters of LNG in liquid form, or about 3.0 billion cubic feet. As of early 2005, there were 177 LNG tankers worldwide.
When an LNG tanker arrives at a receiving terminal, the LNG is transferred to storage tanks. These tanks are built either above or below ground. These are very robust structures. Their doubled-walled construction makes them essentially a "tank within a tank." The outer tank is typically constructed of carbon steel, while the inner tank is usually nine percent nickel steel. Between the two tanks is extremely efficient insulation to keep the cryogenic liquid sufficiently cold.
Each U.S. import terminal is equipped with storage tanks capable of holding at least one tanker load of LNG. Newer and expanded facilities will likely have a capacity closer to two tanker loads.
LNG is converted back into its gaseous form at the terminal when it is sent into the nation's gas pipelines. To convert LNG back into its original gaseous state, it is fed into a regasification plant.
Worldwide (as of February 2005) there were 18 LNG liquefaction plants exporting LNG and 45 LNG import terminals.
The oldest liquefaction plant in the United States was constructed in Kenai, Alaska, in 1969 and is still active. Owned by ConocoPhillips and Marathon Oil, the terminal exports LNG to Japan.
The United States currently has four marine onshore receiving terminals located at Elba Island, GA; Cove Point, MD; Everett, MA; and Lake Charles, LA, and one offshore terminal, the Gulf Gateway Energy Bridge in the Gulf of Mexico. (There is a sixth U.S. import facility in Puerto Rico.) LNG imports into the United States began with the construction of the Everett, MA, terminal in 1971. Construction of the Cove Point and Elba Island terminals followed in 1978, while the terminal at Lake Charles was completed in 1982.
Higher U.S. natural gas prices in recent years have stimulated plans for expansion and new construction of LNG marine terminal facilities. In addition to the expansion plans at the four existing LNG import facilities in the Lower 48 States, more than 35 proposals have been put forth to serve North American markets.
Although the tanks at an LNG marine terminal may function as storage tanks for peak periods of gas demand, the principal operation of an import terminal is not for gas storage, but rather for receiving the water-borne LNG imports and then regasifying LNG for shipment via pipelines to customers. Consequently, the LNG may be in storage at a marine import terminal for only a few days and is seldom held for more than a few months.
In addition to marine LNG terminals, the United States has more than 100 other active LNG facilities including storage, regasification, and operational facilities in niche markets. An example of a niche market application is the storage of LNG by some utilities to meet peak natural gas demand periods, typically the coldest days of the year. LNG is a key element of the nation's gas supply in areas such as the Northeast where underground storage is not feasible. For example, LNG provides as much as 40% of natural gas supply for the New England area during peak winter demand periods.
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