WHAT IS LIQUEFIED NATURAL GAS (LNG)?
When natural gas is cooled to the point of liquefication, which happens at -162° celsius, it becomes Liquefied Natural Gas. Its abbreviated label is LNG.
It is odourless, colourless, non-corrosive, non-toxic, non-corrosive and non-flammable. It is also much more dense than gaseous natural gas; taking up about 1/600th of the space that the same amount of gaseous natural gas would take up.
This significant volume reduction makes LNG much more efficient and cost effective to both transport and store than regular natural gas.
HOW IS LIQUEFIED NATURAL GAS (LNG) CREATED?
When natural gas is cooled to -132° Celsius, (-260° Fahrenheit), liquid natural gas (LNG) is created. The natural gas transforms from a vapour to a liquid.
It is a form of methane. During the cooling process the other components of natural gas such as water, carbon dioxide, nitrogen, oxygen, sulfur compounds, and other hydrocarbons are gradually removed, which leaves almost pure methane.
During the transformation process the volume of the gas is compressed 600 times. This makes it more economical to store for later use, or to ship longs distances from countries with an abundance of natural gas to those starved of the fuel.
Though Liquefied Natural Gas is considerably denser than gaseous natural gas, it is nevertheless much lighter than water by volume; weighing less than half the weight of water. In fact it will float if it is spilled on water.
The lightweight yet highly energy dense nature of LNG makes it very efficient to transport, usually in large, ocean-going tankers which have double hulls for extra insulation designed to help keep the liquid natural gas cold.
WHAT COUNTRIES IMPORT LNG?
There are 91 LNG receiving terminals located worldwide. Japan, South Korea, and a number of European Countries import LNG. The United States still imports small amounts of LNG, but far less than it did prior to the current increases in shale gas production. (Source: Bureau of Economic Geology, University of Texas at Austin, Introduction to LNG.)
In 2019 South Africa and Mozambique will be joining the list of countries with receiving terminals.
WHAT IS LIQUEFIED NATURAL GAS (LNG) USED FOR?
LNG has many uses. LNG can be turned back into natural gas in a process called re-gasification, and then distributed using conventional means such as pipelines. It can also be used to power vehicles.
It is particularly attractive as a transport fuel as it burns cleaner than petrol and diesel, reduces vehicle maintenance needs and cuts greenhouse gas emissions by as much as 30%-40%. Additionally, LNG fuel allows more energy to be stored onboard the vehicle in a smaller space.
LNG, once re-gasified, and back to is natural gas state, can be used in same traditional ways as natural gas: heating, fuel for cooking and household appliances. It is also often used for on-site power generation.
WHAT ADVANTAGES DOES LNG OFFER?
LNG is very efficient to transport. That makes it possible for natural gas deposits that are isolated from infrastructure such as pipelines, to have their product recovered and transported via tankers.
LNG tankers are also very safe. LNG is not flammable nor explosive as a liquid. When it begins to vaporize it is potentially flammable and explosive, but only within the range of 5% – 15% natural gas in air.
At less than 5% there is not enough natural gas to burn, while at more than 15% there is not enough oxygen to burn.
LNG also allows for convenient storage of natural gas during off-peak times. This is called “peak-shaving” and it refers to the storage of surplus natural gas in LNG form during periods of lower energy consumption.
Once energy demands rise, then it can be re-gasified and used to help meet the higher demand. This helps prevent energy shortages.
WHERE DOES LNG COME FROM?
A majority of the world's LNG supply comes from countries with large natural gas reserves. These countries include Algeria, Australia, Brunei, Indonesia, Libya, Malaysia, Nigeria, Oman, Qatar, Trinidad and Tobago and United States.
HOW IS LNG TRANSPORTED?
LNG is transported in double-hulled ships specifically designed to handle the low temperature of LNG. These carriers are insulated to limit the amount of LNG that boils off or evaporates. This boil off gas is sometimes used to supplement fuel for the carriers. LNG carriers are up to 305 metres long and require a minimum water depth of 12 metres when fully loaded.
HOW IS LNG STORED?
When LNG is received at most terminals, it is transferred to insulated storage tanks that are built to specifically hold LNG. These tanks can be found above or below ground and keep the liquid at a low temperature to minimize the amount of evaporation. LNG is characterized as a cryogen, a liquefied gas kept in its liquid state at very low temperatures. The temperature within the tank will remain constant if the pressure is kept constant by allowing the boil off gas to escape from the tank. The vapour from the boil off is automatically re-liquefied. This is known as auto-refrigeration. The boil-off gas is collected and used as a fuel source in the facility or on the tanker transporting it.
WHY USE LNG?
Natural gas is the cleanest burning fossil fuel. It produces less emissions and pollutants than either coal or oil. Since LNG occupies only a fraction (1/600) of the volume of natural gas, and takes up less space, it is more economical to transport across large distances and can be stored in larger quantities. LNG is a price-competitive source of energy that could help meet the future economic of South Africa.
IS LNG FLAMMABLE?
When cold LNG comes in contact with warmer air, it becomes a visible vapor cloud. As it continues to get warmer, the vapor cloud becomes lighter than air and rises. When LNG vapor mixes with air it is only flammable if within 5%-15% natural gas in air. Less than this is not enough to burn. More than this, there is too much gas in the air and not enough oxygen for it to burn.
IS LNG EXPLOSIVE?
As a liquid, LNG is not explosive.