LNG Supply

What is LNG ? LNG, which stands for Liquefied Natural Gas, is natural gas that has been converted to a liquid state by cooling to below -163°C. In this form, it occupies 600 times less space than before cooling, while retaining the same calorific value. This makes transport much easier. Setting up a LNG chain requires investment in several types of facility: 1. Exploration, to detect deposits of natural gas (which are generally discovered during oil exploration operations) and extraction/production 2. Storage then liquefaction, to convert the natural gas from “gaseous” to “liquid” form in which it can be transported by tanker 3. Transportation by special vessels called LNG tankers 4. Storage then regasification, to restore the natural gas to its gaseous form, in which it can be transmitted through pipelines for consumption by end customers.

The LNG supply chain

A LNG supply chain is made up of 4 interdependent segments: exploration/production, liquefaction, transportation and regasification. Each of these segments has its own specific industrial processes and involves specific rules and participants.
1. Exploration – production
At the heart of this essential activity, specialists analyse geological structure to identify areas that may contain hydrocarbons. They carry out special tests, such as seismic analysis, to confirm their initial assessments. Drilling is undertaken when there is a high probability of discovering gas (or oil). If the well is viable (after a series of tests, measurements and additional drilling), it can go into production.
2. Liquefaction
The natural gas extracted from the deposit is filtered and purified, so as not to damage equipment during the conversion from gas to liquid, and in order to meet the specifications of the importing regions. This means that the liquefaction process produces a natural gas with a methane content close to 100%. Liquefaction plants often consist of several installations arranged in parallel, called “liquefaction trains”. The liquefaction process reduces the volume of gas by a factor of around 600, in other words 1 cubic metre of LNG at -163°C has the same energy content as 600 cubic metres of “gaseous” gas at ambient temperature and atmospheric pressure. The density of LNG is around 45% that of water.
3. LNG transportation
LNG tankers are double-hulled ships specially designed to prevent hull leaks and ruptures in the event of accident. The LNG is stored in tanks (generally 4 to 5 per tanker) at a temperature of -163°C and at atmospheric pressure. There are currently 3 types of LNG carrier, each corresponding to a different tank design: membrane tanks, spherical tanks and IHI Prismatic tanks. In 2009, carriers with membrane tanks accounted for more than 60% of world LNG transportation capacity, and more than 85% of orders. This is so far the only technology which allows the construction of large capacity carriers such as the Q-flex (210,000 cu. m.) and Q-max (260,000 cu. m.) vessels.
4. Storage and regasification
Once received and offloaded, the liquefied natural gas is returned to cryogenic storage tanks – usually varying in capacity from 100,000 to 160,000 cubic meters, depending on the site – where it is kept at a temperature of -163°C prior to regasification. Regasification consists of gradually warming the gas back up to a temperature of over 0°C. It is done under high pressures of 60 to 100 bar, usually in a series of seawater percolation heat exchangers, the most energy efficient technique when water of the right quality is available. An alternative method is to burn some of the gas to provide heat. On its way out of the terminal, the gas undergoes any treatment processes needed to bring its characteristics in line with regulatory and end-user requirements. Its heating value, for example, may be tweaked by altering nitrogen, butane or propane content or blending it with other gases.