Liquefied Natural Gas (LNG) is natural gas that has been cooled to -161 degrees Centigrade. Natural gas is made up mainly of methane, with low concentrations of other hydrocarbons such as ethane, propane and butane. It also contains water, carbon dioxide, nitrogen, oxygen and some sulfur compounds. Most of these additional compounds are removed during the liquefaction process. The remaining gas is primarily methane with only low quantities of other hydrocarbons.
In its liquid state, LNG is reduced to approximately one-six hundredth (1/600th) of its volume compared to the gaseous form. This makes it easier to be stored and transported safely and reliably to all corners of the globe. LNG is an odourless, colourless, non-corrosive and non-toxic liquid and is stored and transported at an atmospheric pressure equivalent to its boiling point, meaning its temperature stays constant as long as it is maintained at a constant pressure.
Because natural gas is colorless, odorless and tasteless, a chemical called mercaptan (that has a sulfur like odor) is added before distribution, to give it a distinct unpleasant odor (like rotten eggs). This serves as a safety device by allowing it to be detected in the atmosphere, in the event of a leak.
Millions of years ago, the remains of plants and animals decayed and built up in thick layers. This decayed matter from plants and animals is called organic material. Over time, the mud and soil changed to rock, covered the organic material and trapped it beneath the rock. Pressure and heat changed some of this organic material into coal, some into oil (petroleum), and some into natural gas - tiny bubbles of odorless gas. The main ingredient in natural gas is methane, a gas (or compound) composed of one carbon atom and four hydrogen atoms.
The search for natural gas begins with geologists (people who study the structure of the earth) locating the types of rock that are usually found near gas and oil deposits.
Scientists and engineers explore a chosen area by studying rock samples from the earth and taking measurements. If the site seems promising, drilling begins. Some of these areas are on land but many are offshore, deep in the ocean. Once the gas is found, it flows up through the well to the surface of the ground and into large pipelines.
At an offshore production platform, the gas and associated gas condensate (heavier hydrocarbons in liquid form) are separated and the condensate stabilised, before the processed gas is transferred to shore with the associated condensate via an undersea pipeline, and the gas becomes the feedstock for the onshore LNG plant.
For countries where the gas is used in local markets, it is technically and economically viable to transport the gas through pipelines, an option that is used to deliver Russian natural gas to European markets, and Canadian gas to U.S. markets. When transport through pipelines isn’t possible, as is the case in Qatar when our main markets are many thousands of kilometres distant, liquefying the gas is the preferred option for ease of transportation.
The gas then flows into a liquefaction train for processing into LNG. A production “train” is a self-contained processing unit, the complex line up of compressors, turbines, vessels and interconnecting pipework that liquefies the gas to turn it into LNG. During the first phase of this process impurities in the gas—sulfur compounds, carbon dioxide and water—are removed in stages.
The gas is then chilled by means of propane and mixed refrigeration process. The heavy hydrocarbons are separated out and fractionated into liquefied petroleum gas (LPG) and plant condensate. The main heat exchanger in each train then cools the gas to about 150 degrees, using a mixed refrigerant system, liquefying it in the process.
Finally, as the temperature decreases to minus 162 degrees, nitrogen is removed. The liquefied natural gas (LNG) is then piped to one of four storage tanks ready to be loaded onto the purpose-built LNG tankers.
Each of the four LNG tanks has a one-meter thick concrete wall with a fully insulated inner-steel lining to maintain the LNG at minus 160 degrees Celsius (minus 260 degrees Fahrenheit). The capacity of each tank is 85,000 cubic meters and the combined capacity of the four tanks is equivalent to about five days of plant production. The LNG is transported to markets in special LNG tankers.
To ship LNG to customers in Japan and Spain Qatargas currently has a fleet of 11 purpose-built vessels, each with a capacity of 135,000 cubic meters (4.8 million cubic feet) stored in five Moss-Rosenberg design spherical LNG tanks. Used to transport LNG from Qatargas to its Japanese buyers, each makes a return voyage between Qatar and Japan approximately once a month.
Currently, in step with the development of Qatargas 2, 3, and 4, Qatargas is pioneering the development of two new classes of LNG tankers. Known as Q-Flex and Q-Max class ships, they offer a quantum leap in the capacities and capabilities of LNG carriers. Each ship will have a cargo capacity of between 210,000 and 266,000 cubic metres, and are 80% larger than the current LNG fleet.
At the respective destinations, the LNG is transferred ashore and regasified, that is turned back into gas, by reheating the LNG until it regains its gaseous form. The regasification plant is connected to storage facilities and pipelines. It is then ready for distribution as the energy of choice for businesses and homes in major markets around the world.
The natural gas business uses many different measures, depending on whether you want to measure LNG’s volume, its energy content, or if it is in gas or liquid form. The main measures we use in this website is (mtpa millions of tones per annum), which measures the amount of LNG we produce at our facilities each year.
When natural gas is extracted from under the seabed, it is a mix of a number of different naturally occurring components, often in minute quantities. During the liquefaction process, these other components are separated out. Because of the vast quantities of gas involved, they have become viable by-products which we process and ship to different markets, including LPG, sulfur and helium.
LNG is increasingly becoming the fuel of choice for energy utilities around the world due to its clean-burning qualities and lower CO2 emissions per unit of energy, together with its high-energy efficiency when used to generate power in combined cycle power stations.