Natural gas was once a fuel which was only really usable when found in easy-to-access locations or areas which could be connected up to a pipeline for transportation to the end user. LNG innovation in the shape of cryogenic storage solutions has changed all that – and looks set to change the face of the modern energy market for good.
Common applications of LNG
LNG, short for Liquefied Natural Gas, is used in a range of ways. Its primary role at the moment is to facilitate the transportation of natural gas to the market by transforming the natural product from gaseous state to a liquid state by cooling to extremely low temperatures.
Some gas fields are located in areas where the natural environment makes it prohibitively expensive – or simply impossible in engineering terms – to install a network of pipelines. This is often the case at sea. In its liquid form, this key fuel can be transported to any port in the world with the right facilities to handle LNG tankers. Once dry land is reached, it can be regasified and introduced into the gas distribution network. Sometimes LNG is also used to ‘top up’ gas networks at times of peak demand.
A minor – but growing – share of the LNG market is going towards transportation. The first LNG-powered container ship, the Isla Bella, was launched in California in 2015. Since then, hundreds of LNG-fuelled ships have been built or ordered. In addition to ships, LNG is also being used to power large lorries and even trains!
Cryogenic engineering: the cornerstone of the LNG revolution
Without the development of technology to supercool natural gas and maintain it at extremely low temperatures in the form of LNG, this component of the energy market wouldn’t even exist.
In order to condense, natural gas needs to be cooled to – 162 °C. The plant that carries out this task is called an LNG train. After the removal of various pollutants and heavy hydrocarbons, we move onto the liquefaction stage. This is achieved through refrigeration cycles, where pre-treated gas is cooled using cryogenic heat exchangers. The precooled mixed refrigerant cycle is the most commonly used cycle in the LNG field.
Once the gas has been cooled sufficiently to reach liquid form, it has to be kept cold. This is where cryogenic storage technology comes into its own. LNG storage tanks are characterized by having two containers and may be classed as single, double or full containment systems. The base, roof and sidewalls of these tanks are insulated using various materials. Despite this insulation, small amounts of LNG evaporate within the tank, creating what’s called BOG (boil-off gas). This gas can be reliquefied or compressed and removed, ensuring pressure and therefore temperature in the tank is kept at a constant level. This process is called ‘auto-refrigeration’.
Cryogenic technology has even been extended to LNG STS operations, as we’ll see very soon.
Technical innovation in the LNG field
One of the most exciting developments in the field of LNG innovation has to be floating liquefaction. FLNG facilities process natural gas directly at source at sea, without the need to install expensive, environmentally disruptive pipeline infrastructure. All of the pre-treatment and liquefaction processes carried out in an LNG train on land can be replicated here, before the finished product is transferred to waiting carriers. This more cost-efficient approach opens up gas fields which in the past would not have been economically viable.
One remarkable piece of equipment that’s key to LNG STS operations (ship-to-ship transfers) is the cryogenic loading arm. These are used to transfer LNG between ships or between FLNGs and ships and have to be constructed to cope with the incredibly low temperatures required for LNG operations.
LNG STS operations are very complex due to the constantly changing environment in which they take place (sea and weather conditions). This requires other technologies to be brought to bear, such as simulators which can be used for anything from training ships’ crews to forecasting optimal windows for STS transfers.
The most common approaches to transporting liquified natural gas
By far the biggest proportion of LNG transportation takes place via the world’s oceans in large vessels called LNG carriers. These have grown steadily in both number and size since the 1950s and the largest vessels can now carry up to 266,000 cubic metres of LNG.
Once onshore, the LNG will be eventually regasified and introduced into the distribution network or alternatively, it can be transferred to specialist LNG tanker lorries and trucks to take it to destinations lacking pipelines.
Rail transportation of LNG is less common but is slowly becoming more widespread. France saw its first LNG rail delivery in 2021, destined for a service station in northern Italy! Trials using specialized tank rail cars have also been carried out in Germany. It’s a classic example of LNG innovation in action once again, this time in its transportation!