LNG at a glance

LNG is produced from natural gas in the liquefacation process. Liquefacation or condensation is a phenomenon that changes the aggregate state, when a substance passes from the gas phase into the liquid phase. This can take place under certain pressures and at a temperature below the critical temperature of the surroundings. Condensation is connected with reducing the distance among the molecules of a given substance. The drop in temperature makes the molecules move slower.

The forces acting among them increase until they reach their new state of equilibrium. Heat energy is given out in this process. The liquefacation process takes place in a different manner when the gas contains impurities.

The main component of natural gas is methane. Apart from methane, it also contains ethane and propane as well as heavier hydrocarbons such as nitrogen, oxygen, carbon dioxide and sulphur. During the liquefacation process, natural gas has to be purified mainly from water and carbon dioxide in order to prevent particle matter forming when the gas is cooled to a temperature of approx. -160°C. In effect, LNG is a very pure gas – comprised of 95% methane, and only 5% of other components.

There are three basic liquefaction methods*:

1. Classic cascade cycle. The natural gas purified of carbon dioxide and water is passed under appropriate pressure through the facility and is cooled in three cooling cycles, in which the cooling agents are propane, ethane and methane. Propane from the first cycle is simultaneously used to liquefy ethane from the second cycle, whereas ethane from the second cycle is used to cool the methane in the third cycle. An advantage of this method is that it is a relatively energy saving process. A disadvantage is the large amount of facilities necessary for the process to take place, as well as the large quantities of pure ethane propane needed.
2. The cascade cycle with a mixed cooling factor. This is a modification of the classic cascade system with the use of only one compressor and one cooling agent constituting a mixture of hydrocarbons. Natural gas is firstly cooled with the use of the propane cooling cycle, and then cooled with the mixture of hydrocarbons. This method is a little more energy consuming than the classic cascade system, however, its advantage is the smaller number of facilities necessary to carry out the process. Due to the lower operating costs, different variants of this method are applied more frequently than the classic cascade system.
3. Decompression cycle with the use of a turboexpander. The gas liquefacation facilities with the use of the method based on the decompression cycle work in a similar way to Joule’s and Thompson’s classic method and facilities producing liquid oxygen and nitrogen with the use of low-temperature air fractioning. In this process, a portion of the gas is decompressed in a machine called a turboexpander, and then cooled to a very low temperature. The cooled gas is then used to liquefy another portion of gas flowing through the facility. This method is relatively simple and does not require large investment outlays. However, it is characterised by a large consumption of energy necessary to compress the gas. Due to this, this method is used in locations where the energy required to compress the gas is cheap. It is most recommended in case of small gas liquefacation facilities for covering peak demands.
    

*Source: Jacek Molenda “Gaz ziemny. Paliwo i surowiec." [Natural gas. Fuel and Raw Material], Wydawnictwo Naukowo-Techniczne, Warsaw 1996.

The re-gasification of LNG consists in returning the gas from its liquefied state to its gas state by heating the liquefied raw material. Evaporators of various output volumes, constructions and heating methods are the basic equipments used in the LNG re-gasification facility.

LNG evaporators are divided into the following groups:

• Evaporators with heating to a temperature equivalent to the temperature of the surroundings:
  • evaporators heated by air (ORV),
  • evaporators heated by sea or river water (SPV).
• Evaporators with heating to a temperature higher than the temperature of the surroundings:
  • evaporators with direct heating,
  • fire/furnace heating – gas burners,
  • electric heating.
• Evaporators with direct heating with the use of heat carrier:
  • water steam heaters,
  • water heaters heated by immersed gas burners,
  • isopentane heaters or other energy carriers.

The location, intended purpose and fuel availability (or heating factor) is decisive in selecting the type of evaporators and the LNG re-gasification facility scheme.

The growing significance of LNG in the past few years is connected with the overall increase in demand for natural gas.

The use of liquefied natural gas is spurred by the development of transport possibilities of LNG, and above all the expansion of the methane transporter fleet (204 units in 2006 – data according to: The Maritime Business Strategies data, LLC; by 2010 another 145 ships will be built), as well as the large price competitiveness of LNG in relation to gas transported via pipelines.

The location of gas deposits throughout the world in places which are difficult to connect using pipelines with countries, who are the chief recipients of that gas, also has a vast significance on the increasing interest in LNG. The use of liquefied natural gas is also an excellent method for covering the peak demands for gas.

Basic advantages of LNG:

• Flexibility of supplies – LNG is a proven method both in terms of being an effective way of diversifying gas supplies for certain countries as well as covering the peak demand for gas.
• Output – during the liquefacation of natural gas into LNG, its capacity is reduced by approx. 600 times. This means that after re-gasification from 100 m³ of LNG we receive 60,000 m³ of natural gas.
• Economy – the costs of transport and storage of LNG are smaller than that of natural gas. This affects, among others, the possibility of selecting suppliers from different parts of the world (cost of purchase and transport optimisation).
• Ecology – natural gas is an ecological fuel. It emits much less pollutants into the atmosphere during combustion than coal, petroleum or other mined fuels. Liquefied natural gas is additionally purified – it is comprised of 95% methane with a small fraction of other components (approx. 5%). LNG is therefore a very clean fuel without toxic or corrosive properties.
• Security – should a leak possibly occur, LNG simply evaporates and is rarefied in the atmosphere. Thus, it is a much less harmful and dangerous fuel than petroleum or LPG. It is impossible to pollute the environment (sea, soil) in the case of an LNG leak. Modern technologies used in constructing the LNG containers (the 'full-containment', type), as well as special procedures and security systems ensure an exceptionally high level of safety of the re-gasification terminals.

Some examples of how LNG can be used:

• Supplying natural gas to final customers. LNG is used as an alternative to gas supplied via traditional gas pipelines. In some countries, this is a method for the diversification of gas supply sources and ensuring energy independence.
• Covering short-term peak demand for gas for 3 to 4 weeks during a year with the aid of facilities liquefying natural gas from pipelines or facilities supplied by external sources, e.g. from the LNG facility to the low-methane natural gas conversion facility, or from transportable complex facilities. European countries that have implemented such solutions include Germany, Great Britain, the Netherlands and Belgium. This solution is also widely used in the USA where several dozen facilities are in operation for the liquefacation of natural gas and re-gasification, as well as LNG storage.
• Supplying gas to customers previously unconnected to the gas network (distribution) – so called ‘white spots’. Usually one or several large industrial customers are connected to an LNG station, while the remainder constitutes smaller communal customers.
• Supplying gas to small and medium towns to which fuel is delivered from ‘LNG satellite facilities’, which in turn obtain the liquefied natural gas from larger liquefacation facilities. Examples of such solutions can be found in Germany and Great Britain.
• Fuel for driving vehicles: buses, railway engines, helicopters, and supersonic planes. Interest in liquefied natural gas as a fuel for engines is particularly high in countries with a large population density. This results from the need to protect the environment from the toxic components of car exhaust emissions. This solution has been implemented in France, Great Britain and Japan.
• Fuel for power plants. Supplying energy to power plants with the use of LNG is widely applied throughout Japan - the power plant in Jokohama is fuelled by liquefied natural gas supplied from tankers from Alaskan deposits.
• Supplying gas to customers that are temporarily cut off from pipeline gas supplies, for example, due to the necessity of conducting repair works or conservation of the transmission network. The use of LNG enables customers to be supplied with gas on an uninterrupted basis. The solution is implemented in France, among others.
• Source of cold - LNG is also used for cooling purposes and for rarefying the air, for instance, in megeto-gasodynamic generators for cooling magnets or in the refinery and petrochemical industry in low-temperature facilities for fractionation of hydrocarbon gases. The cold emitted during the LNG re-gasification process is frequently used in low-temperature facilities like those for the production of oxygen by fractional distillation of liquefied air. The facility in Fos-sur-Mer in France operates in this way. 
• Supplying fuel cells generating electricity and/or heat. Examples of such use can be found in France.

The first liquefacation of gas, id est transformation of the gas state into the liquid state was performed by a British physicist and chemist Michael Faraday (1791–1867).

In 1883, two professors from the Jagiellonian University - Zygmunt Wróblewski and Karol Olszewski – managed to liquefy oxygen and nitrogen from atmospheric air. However, cooling and liquefacation technologies that can be implemented in cooling equipment were patented in 1896 by a German engineer and entrepreneur Karl Paul Gottfried von Linde, who in 1873 constructed the first cooling equipment in Europe.

However, the first cooler in the world appeared in Australia and was designed and built by a Scotsman - James Harrisson, printer and journalist by profession. The original technological concept served to cool the air and was put into use for the first time in the foods sector.

The cooling and liquefacation technology of natural gas was implemented for the first time in the United States. The first facility for liquefying LNG was opened in western Virginia in 1917, and the first commercial liquefacation facility was constructed in Cleveland, Ohio (USA) in 1941.

The first transport of Liquefied Natural Gas took place after the Second World War. In January 1959, “The Methane Pioneer", an adapted transporter ship that was used in the Second World War, sailed out of Lake Charles in Louisiana (USA) with a load including LNG, in order to reach its destination - Canvey Island in Great Britain.

After the first and subsequent seven successful transports of LNG via ships, the British Gas Council decided to import LNG from Venezuela. However, in connection with the discovery of deposits in Libya and Algeria, countries located much nearer Great Britain than Venezuela it was ultimately decided to import LNG from Algeria, which thus became the first exporter of LNG in the world. The first commercial delivery of LNG from Algeria to the British market took place in 1964. LNG supplies to Great Britain did not withstand the competition with deposits discovered in the North Sea.

The 70’s and 80’s brought a heightened interest in LNG. In Asian countries, mainly Japan and Korea, the construction of power plants were commenced which were intended to be fuelled by natural gas. This significantly contributed to better conditions for harnessing LNG