BASF and Samsung Heavy Industries have developed a blanket made of foam cubes to prevent liquefied natural gas from sloshing during its transport in tankers.
Each cube, with sides of 1 meter, is made of two blocks of Basotect, BASF’s open-cell foam made from melamine resin. Basotect has high acoustic and good heat-insulation properties and is both flame-retardant and resistant to many chemicals, BASF says.
A type of buoy is placed between the two blocks so that the Basotect cube does not submerge more than 80 percent even after becoming fully soaked with LNG. The individual cubes are stitched into Vectran textile covers and secured to one another with Vectran belts.
Vectran, which is made from polyarylate fiber, is produced by the Japanese company Kuraray, and is also suitable for use under cryogenic conditions. In addition, Vectran is durable and abrasion-resistant, BASF says.
LNG tankers contain three to five tanks and each tank can hold around 40,000 cubic meters of liquefied gas. These steel tanks must remain cooled to minus 162 degrees Celsius at all times. In addition to this challenge, all ships that carry liquids must address the problem of sloshing, which even mild seas can cause. As a consequence, LNG tankers can only travel when full (loaded over 80 percent) or empty (loaded under 10 percent). It has thus far not been possible for LNG tankers to have flexible load levels.
Anti-sloshing blankets are good for the environment, the companies say. Because LNG tankers will be able to take different load levels, it will be possible for them to call at several harbors in succession and to unload their contents based on need. This will reduce the number of no-load journeys and costs, while reducing emissions and fuel.
BASF says the anti-sloshing blanket consists of many individual elements because it has to be flexible and mobile to best accommodate and reduce wave action. These individual elements should be secured together at the shipyard, directly inside the tanks, before the tanker is filled with LNG for the first time. The blankets can be placed in the tanks before they are loaded, and remain there after they are emptied. Tests at BASF’s technical laboratory have shown that when the containers are emptied, Basotect releases nearly all of the LNG it has absorbed.
The Basotect blanket has also been tested in South Korea by the departments of naval architecture and ocean engineering at Seoul National University and Pusan National University. Tests showed that the Basotect blanket was able to considerably reduce sloshing and reduce peak pressures against the walls by about one-fifth.
Because there is less sloshing, shipbuilders can also eliminate two corners of the octagonal shape and thus have right angles at the top of the tank. This means that about 5 percent more LNG can be stored and the production cost can be saved in the simplified tank shape, BASF says.
The blanket also lowers the boil-off rate, or vaporization, thus improving safety and increasing the amount of liquefied gas that arrives at the harbor.
