Liquefied natural gas, or LNG
Liquefied Natural Gas, or LNG, is natural gas in its liquid form. When natural gas is cooled down to minus 259 degrees Fahrenheit (or -161 degrees Celsius), it becomes a clear, colorless, odorless liquid. Natural gas in liquid form, is only one six-hundredth of the volume of its gaseous form, which makes it easier to be stored and transport.
The natural gas is primarily Methane, with low concentrations of other Hydrocarbons, water, Carbon dioxide, nitrogen, oxygen and some sulfur compounds. During the process known as liquefaction, the natural gas is cooled down below its boiling point, and in the process removing most of these additional compounds. The remaining gas is primarily methane with only low amounts of other hydrocarbons.
Liquefied natural gas weighs less than half the weight of water so it will float if spilled on water.
LNG import and transport
A large part of the world’s LNG (Liquafied Natural Gas) supply comes from countries with large natural gas reserves. These countries include Algeria, Australia, Brunei, Indonesia, Libya, Malaysia, Nigeria, Oman, Qatar, and Trinidad and Tobago.
There are more than 40 gas receiving terminals located worldwide. Japan, South Korea, the United State and a number of European Counties are importors of LNG.
LNG is normally transported in double-hulled ships specifically designed to handle the low temperature. These carriers are insulated to limit the amount of LNG that boils off or evaporates. This boil off gas is sometimes used to supplement fuel for the the carriers. LNG carriers are up to 1000 feet long, and require a minimum water depth of 40 feet when fully loaded. There are currently 136 ships which transport more than 120 million metric tons of LNG every year. (Source: University of Houston IELE, Introduction to LNG.)
Storage of LNG
When LNG is received at most terminals, it is transferred to insulated storage tanks that are built to specifically hold LNG. These tanks can be found above or below ground and keep the liquid at a low temperature to minimize the amount of evaporation. If LNG vapors are not released, the pressure and temperature within the tank will continue to rise. LNG is characterized as a cryogen, a liquefied gas kept in its liquid state at very low temperatures. The temperature within the tank will remain constant if the pressure is kept constant by allowing the boil off gas to escape from the tank. This is known as auto-refrigeration. The boil-off gas is collected and used as a fuel source in the facility or on the tanker transporting it. When Natural Gas is needed, the LNG is warmed to a point where it converts back to its gaseous state. This is accomplished using a regasificationprocess involving heat.
Natural gas may be stored in a number of different ways. It is most commonly stored underground under pressure in three types of facilities. The most commonly used in California are depleted reservoirs in Oil and/or gas fields because they are more available. Aquifers and salt cavern formations are also used under certain conditions. The characteristics and economics of each type of storage site will dictate its suitability for use. Two of the most important characteristics of an underground storage Reservoir are its capability to hold natural gas for future use and its deliverability rate. The deliverability rate is determined by the withdrawal capacity of the associated valves and compressors and the total amount of gas in the reservoir. In other states, natural gas is also stored as LNG after the natural gas has been liquefied and placed in above-ground storage tanks. (Source: U.S. Department of Energy, Energy Information Administration.)
Use of LNG
LNG is normally warmed to make Natural Gas to be used in heating and cooking as Wellas electricity generation and other industrial uses. LNG can also be kept as a liquid to be used as an alternative transportation fuel.
Natural gas is the cleanest burning fossil fuel. It produces less emissions and pollutants than either Coal or Oil. The North American supply basins are maturing and as demand for natural gas increases in California and throughout the United States, alternative sources of natural gas are being investigated. Natural gas is available outside of North America, but this gas is not accessible by pipelines. Natural gas can be imported to the United States from distant sources in the form of LNG. Since LNG occupies only a fraction (1/600) of the volume of natural gas, and takes up less space, it is more economical to transport across large distances and can be stored in larger quantities. LNG is a price-competitive source of energy that could help meet future economic needs in the United States.
All LNG ships must comply with all pertinent local and international regulatory requirements, which include regulations and codes set forth by the International Maritime Organization (IMO), the U.S. Maritime Administration (MARAD), the U.S. Coast Guard (USCG), and the U.S. Department of Transportation (DOT), as Well as the hosting Port Authority.
DOT regulations must be followed at onshore LNG facilities and marine terminals. The Research and Special Programs Administration, DOT, regulations include 49 CFR Part 193 – Liquefied Natural Gas Facilities: Federal Safety Standards. These standards specify siting, design, construction, equipment, and fire protection requirements that apply to new LNG facilities and to existing facilities that have been replaced, relocated, or significantly altered.
Offshore marine terminals must follow regulations set by the USCG. The USCG monitors the safety of coastal waters around the U.S. and ensures the safety of ships while in U.S. waters and in port by preventing other ships from getting near LNG tankers. The USCG works with local harbor authorities and LNG facility personnel to ensure that proper procedures are followed. The USCG and MARAD are the federal agencies responsible for siting off-shore LNG facilities and are currently developing regulations.
Sources: California Energy Commision