The natural gas reserves in the world are huge, but most of the deposits are located in remote places remote from industrial areas. This is not so bad - you can lay a pipeline on land or on the bottom of the sea. And for transportation across the ocean, gas is transferred to a liquid state. At the same time, the volume decreases by almost six hundred times, which makes it possible to use not only pipelines, but also specially designed LNG carriers for gas transportation.
Tankers for the transport of liquefied gases
LNG is natural gas cooled to a temperature of -162 ° C, at which it passes from a gaseous state to a liquid state.
Most of the global export of liquefied natural gas is carried out on the intercontinental market by two types of tankers, denoted by the abbreviations CIS - liquefied petroleum gas and LNG - liquefied natural gas. Specialized vessels differ in the design of tanks and are designed for different cargoes: CIS tankers transport liquefied propane, butane, propylene and other hydrocarbon gases, LNG tankers - methane. Sometimes these tankers are called methane carriers. In the photo below, the image of the tanker in the context.
LNG tanker layout
The main components of the design of a tanker for transporting liquefied gases are power and pumping units, a double hull for extra strength, bow engines, tanks for liquefied gas and powerful refrigeration units to maintain a low gas temperature.
Typically, four to six isolated tanks located along the centerline of the vessel are housed in the hull. The environment of the tanks is a combination of ballast tanks, cofferdams - special compartments to prevent gas leaks from tanks and voids. This arrangement gives the LNG carrier a double hull structure.
Liquefied gases are transported in tanks at pressures that are higher than atmospheric or at temperatures well below ambient temperature. Some tanks use both methods.
Tankers are equipped with tanks under pressure of 17.5 kg / cm 2 . Gas is transported in cylindrical or spherical steel tanks with an appropriate storage temperature. All tankers are built with a double bottom.
Gas tankers are provided with powerful engines and are characterized by high speed. The field of their rational use is long-distance, mainly transcontinental, flights with a length of more than 3,000 nautical miles. Given the active evaporation of methane, the vessel must cover this distance at high speeds.
Tank design features
For the safe transportation of liquefied natural gas, it is required to maintain the temperature in the tanks below -162 ° C and high pressure. Tankers are equipped with membrane tanks with high-vacuum multi-layer insulation. Membrane reservoirs consist of a primary barrier metal layer, an insulating layer, a liquid protective layer, and a second insulating layer. The design of the tanks and the thickness of the metal hull of the tanks depends on the estimated operational pressure, temperature and displacement of the tanker. Under the pressure of sea water, the walls of the tank, being part of the ship, experience the same loads as the hull of the ship.
Liquefied petroleum gases are also transported in spherical metal, well insulated to prevent leakage of tanks under high pressure.
The IGC code defines three types of independent tanks used for transporting gas: A, B and C. LNG tankers are equipped with category B or C tanks, and the tankers of the CIS correspond to category A.
Tanker loading and unloading operations
The most dangerous are tanker loading and unloading operations. Liquefied natural gas is a cryogenic substance whose main component is methane. If it gets into a properly prepared cargo compartment with non-compliance with the temperature regime, a mixture of methane and air becomes explosive.
Tanker loading procedures are strictly regulated. The cargo tank is dried with an inert gas of a certain temperature to prevent the condensation of moist air inside the tank.
After drying the tanks, a hold is blown to remove residual inert gas, after which dry heated air under pressure is supplied to the hold.
Direct injection of liquefied gas is preceded by filling the tank with inert gas to remove air and cool the tanks. The insulation space of the membrane tanks is purged with liquid nitrogen. The loading begins when the gas supply system and the tank are cooled to a temperature close to the temperature of the LNG.
At the destination port, liquefied natural gas is transferred to the onshore tank using a submersible cargo pump installed at the bottom of each cargo tank. When unloading, the requirements for temperature and wet conditions of all lines are also observed in order to avoid the formation of an explosive mixture of methane with air.
Environmental Safety
Strict safety standards are established by the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code). International rules cover almost all aspects of the safety of these ships, as well as crew training standards.
The safety record for transporting liquefied natural gas on ships has a history to be envied. Since 1959, when the commercial transportation of LNG began, there has never been a single death on board related to liquefied natural gas. Eight maritime incidents related to the emergency spill of liquefied natural gas occurred in the world.
In June 1979, the El Paso Kaiser tanker crashed into rocks at a speed of 19 knots with a load of 99,500 m 3 in the Strait of Gibraltar. The vessel suffered severe damage to the bottom along the entire length of the cargo spaces, however, the membrane tanks were not damaged and the liquefied natural gas was not spilled.
Tanker Navigation Through the Straits
Straits are the most dangerous place for navigation, therefore, for the construction of terminals for the production and reception of liquefied natural gas, they choose places on the outskirts of the continents, avoiding complex transport routes and tankers entering the inland seas.
At one time, Ukraine announced its intention to build a terminal for receiving liquefied natural gas in the Odessa region in order to diversify sources of gas supplies to the country. Ankara immediately responded to this.
The constant transit of liquefied natural gas of dangerous goods through the Dardanelles and the Bosphorus on LNG carriers can cause serious environmental damage. These straits are in the top of the most dangerous in the world: the Bosphorus - in third, the Dardanelles - in fifth place. In the event of a major accident, the consequences for the Sea of Marmara and densely populated Istanbul can be disastrous.
International LNG Market
A fleet of specialized vessels links LNG production and regasification plants worldwide to create a safe, reliable and efficient liquefied natural gas transportation network. Methane vessels are equipped with modern leak detection technology, emergency shutdown systems, advanced radar and positioning systems, and other technologies designed to ensure safe and reliable gas transportation.
Liquefied gas currently accounts for more than 35% of the international trade in natural gas, while demand for it is constantly growing.
Some statistics
Today, the liquefied natural gas industry worldwide includes:
- 25 LNG terminals and 89 gas liquefaction plants operate in 18 countries on five continents. Qatar is the world leader in liquefied natural gas production, ahead of Indonesia, Malaysia, Australia and Trinidad and Tobago.
- 93 reception terminals and regasification plants in 26 countries on four continents. Japan, Korea and Spain are leading importers of liquefied natural gas.
- Currently, around 550 tankers are operating around the world for transporting liquefied natural gas.
Leader in the construction of LNG tankers
Historically, about two-thirds of the world's fleet of methane tankers was built by the South Koreans, 22% by the Japanese, 7% by the Chinese, and the rest by France, Spain and the USA. The success of South Korea is related to innovation and price. South Korean builders built the first ice-breaking class methane tankers. They also built the largest Q-Flex and Q-Max LNG tankers with a deadweight of 210,000 and 260,000 cubic meters for the Qatar gas transportation company Nakilat. A distinctive feature of Q-class vessels is the placement of a natural gas liquefaction plant directly on board a giant vessel. The ship is 345 meters long and 53.8 meters wide.
Project "Yamal LNG"
On September 29, 2014, a solemn ceremony of laying the tanker, ordered by the Russian shipping company Modern Commercial Fleet, specializing in the transportation of energy carriers, for the transportation of liquefied natural gas under the Yamal LNG project took place. These are unique Arc7 ice class vessels with the maximum possible dimensions for approaching the port of Sabetta on the Yamal Peninsula.
Intended for the transportation of gas from the South Tambeyskoye field from the Arctic to Europe and Asia and navigation in the harsh climatic conditions of the Arctic, the Yamal LNG tankers are double-acting vessels in design: bow for navigation in open water, and feed for navigation in complex ice setting.
Currently, five such ships have been built. Lead ship Christophe de Margerie . Belongs to Sovcomflot.
On its first commercial voyage, an LNG tanker from Russia set a historical record: for the first time in the history of shipping, a merchant ship passed the Northern Sea Route without an icebreaker.