Imagine if cars could be shrunk. A vehicle the size of a VW Golf would be placed in a refrigerator and after a short time it would only be about 51 cm long, 17 cm high, and 21 cm wide. Refrigerators with shelves for the cars would then be placed on street corners. Although cities would offer more living space, there would no longer be a parking problem. And if you wanted to drive to Italy on vacation, you would take the train. The shrunken vehicles of several vacation trains would fit into a standard 20-ft container used for general freight transport. Over 1,500 shrunken Golfs would fit into such a container. Before use, the car would be reheated and could be used normally. Great idea!
Unfortunately, it is not possible to shrink cars. But it is possible to shrink natural gas - by a factor of 600, which is also the basis for the small car thought experiment. The motivation for shrinking is also the same: to save space for transport and storage. Natural gas is shrunk by cooling it to approximately -162 °C, converting it into a liquid. This is called “liquefied natural gas” or LNG for short.
In Central Europe, pipelines are generally built for gas transport. This allows large quantities of natural gas to be transported economically. However, the cost of construction and operation increases considerably with their length. And the start and end points are fixed. This has the disadvantage that natural gas cannot be traded freely. The use of LNG overcomes this obstacle. The liquefaction of natural gas has enabled the development of a gigantic global infrastructure that meets the gas needs of developed countries in “isolated locations” such as Japan, South Korea, and Taiwan, and satisfies the energy hunger of emerging economies such as China, India, and Brazil. About one-third of the natural gas traded worldwide is “shrunk” before it begins its journey.
As expected, the natural gas is cooled in the exporting countries. The largest of these are Qatar, Australia, Malaysia, and the USA. These countries are home of what are probably the largest refrigeration plants in the world. In Qatar, for example, there are natural gas liquefaction plants, each of which liquefies 7.8 mio t of gas per year. In liquid form, the 7.8 mio t would still fill an aquarium roughly the size of the Alaunpark in Dresden's Neustadt district and as tall as the Dresden TV tower. There are even floating liquefaction units so that gas extracted below sea level can also be liquefied.
For transportation, the LNG is loaded onto special tankers and transported to its destination within approximately 10 – 20 days, depending on the route. What makes these ships so special is their task, which, in terms of temperature conditions, could be roughly translated into our everyday world as follows: as much liquid as possible should remain in a bucket filled with boiling water that has been placed in a pizza oven heated to 280 °C for 10 - 20 days. Anyone who has ever boiled over pasta water in half an hour knows that this is an extremely challenging task. However, engineers benefit from the fact that in huge LNG tanks, the ratio of the surface area through which heat penetrates to the volume of liquid is much smaller than in a bucket of water. Expressed as a percentage, less liquid boils away in the tank simply because it is much larger than the bucket.
However, in order to deliver as much gas as possible to the customer, the tankers are constructed like cool boxes. The insulation layer is 30 - 40 cm thick and consists of PU foam in most of the cases. Inside, the 30 m high tanks are lined with shiny sheets of cold-resistant metal alloys that are welded together. This is because one thing must not happen under any circumstances: the cold liquid must not come into contact with the steel from which the ship's hull is constructed. This is because it is not cold-resistant... Despite good insulation, around 0.15 % of the cargo “boils away” every day during sea transport. This gas is then either used to power the ship or get filled into the refrigeration systems on board that liquefy the gas again.
At the end of its journey, the natural gas is pumped through pipelines into onshore tanks at LNG terminals. A typical tanker transports 150,000 m³ of LNG. Six of such ships loads would be enough to cover the annual heating requirements of the city of Dresden. Before this can happen, however, the LNG must be converted back into gas by adding heat. The coldness of the liquid gas could be used in many ways (e.g., to reduce the energy required to separate air into oxygen and nitrogen or to capture CO₂ from the air), but it is often simply released into the air or seawater.
Depending on how liquefaction, transport, and regasification are technically carried out, 80 - 93 % of the natural gas that was sent on its journey still arrives at the end at the transport chain.
From 2006 to 2009, ILK Dresden was involved in the development of a novel insulation system for LNG tankers.
