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| Fig. 1: A cutaway view of a Moss-equipped LNG carrier. (Source: Wikimedia Commons) |
For much of history, natural gas was regarded as an inconvenient by-product of the oil drilling process. "Flaring," or the burning off of natural gas at an oil well, is a common and highly visible practice at wells focused on extracting liquid fuels. However, thanks to the explosion of global energy demand, as well as the many environmental advantages of natural gas over oil, world consumption of liquefied natural gas has reached 330 billion cubic meters per year - an astonishing 12 quadrillion Btu (1.27 × 1019 joules) of energy. [1] This number has grown at 7.5% annually for the last 20 years. [2] In recent years, revolutions in extraction technology, particularly with regard to shale deposits previously thought unrecoverable, have provided sufficient gas supplies to feed this burgeoning demand. Many of these shale deposits are located in the United States, particularly in Texas and North Dakota, and their productivity has enabled the country to become a net exporter of fossil fuels. Some of these exports travel via pipeline to other nations, but many leave American ports en route to other nations. Natural gas thus exported is liquefied and transported on massive carrier ships.
The natural gas that most homeowners are familiar with emerges as a pointed blue flame atop their stoves, and enables them to cook their scrambled eggs to perfection. This is the useful form of natural gas; however, as gases have a tendency to take up a great deal of space with only minimal mass, efficient transportation of natural gas requires that it become denser. By cooling the gas to a liquid state, carriers achieve a 1/600th volume reduction over gas at atmospheric pressure. [2] Thanks to this precipitous volume decrease, a single large liquefied natural gas (LNG) carrier can transport enough natural gas to satisfy the gas demands of a moderately sized country for weeks. So-called "Q-max" carriers, named for their maximum size which still fits into Qatari terminals, carry up to 265,000 cubic meters of gas - enough to satisfy the LNG demands of California for five years. [2] Safely maintaining massive quantities of volatile fuel at extremely low temperatures (negative 137 degrees Celsius) is no simple task. Ships transporting natural gas are required to be double-hulled, and possess massive and heavily insulated storage tanks to accommodate the gas. [2] A common technology for LNG carriers is the Moss spherical containment system.
Commonly referred to as "ball-in-a-box," the system entails several large spheres containing LNG that make up the majority of a carrier hull, arranged in series. Fig. 1 illustrates this basic design. Tanks are commonly made of aluminum and insulated with polyurethane foam. [2] A spherical design allows for easy fabrication and simple stress analysis and prediction, and the tank is expected to expand and contract in accordance with the pressure imparted by the gas within. As safety is a principal concern, all Moss tanks contain a gas sensor outside the tank shell that detects any leakage. Notably, the vast majority of ships do not possess significant refrigeration or reliquification systems, instead maintaining temperature by insulation; the resulting gas vapors, known as "boil-off," are commonly used to fuel the ship.
The need to store LNG in cryogenic tanks makes the business case for widespread LNG adoption less compelling, especially where pipeline infrastructure exists to transport it more inexpensively. However, the political benefits of widespread American LNG exports are significant. As Russia again emerges as a geopolitical foe, it merits consideration that the Russian economy is heavily dependent upon exports of oil and gas; about two-thirds of Russian exports, and half of Russia's federal budget, derive from such sales. [1] These same exports represent influence in Europe. Numerous Eastern European countries, particularly the Baltic states, have two options for securing natural gas imports: pipelines originating in Russia, and seaborne LNG exports. Ukraine endured a short energy crisis in 2009 when Russia turned off the cross-border pipelines, a sign of the power that derives from energy sales. Russia does not dominate the global energy market, but it can exert strong regional influence in countries whose imports it dominates. Further American investment in LNG technology and carriers can drive down the price of seaborne LNG, making it more practical for these nations to move away from politically risky pipeline imports. This is both a politically and economically sound move; the same investment that helps bring American products to market reduces Russian influence in Eastern Europe.
© Evan Long. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Hearing before the Committee on Energy and Natural Resources to Consider Market Developments for U.S. Natural Gas," United States Senate, S. HRG 112-2215, 8 Nov 11.
[2] S. Mokhatab et al., Handbook of Liquefied Natural Gas (Gulf Professional Publishing, 2013).
