Natural gas is a source of fossil energy, like coal or oil, it is constituted by a mixture of hydrocarbons, molecules formed by carbon and hydrogen atoms. Its calorific value varies greatly according to its composition, but the highest are between 8,500 and 10,200 kilocalories per cubic meter of natural gas.
Natural gas is a primary energy, or that can be obtained directly without transformation. The other primary energies are solar energy, coal and oil. It is the cleanest fossil energy in terms of waste and atmospheric emissions, and the most efficient fuel for obtaining electricity in thermal power plants, with a total efficiency of 50.7% compared to 25.7% of fuel, 26.1% of the uranium (nuclear power plant) and 26.8% of the coal. Its direct use, without having to previously transform into electricity, has a much higher efficiency of 91.2%. It is also cheaper and easier to store than coal and petroleum products.
For all these reasons, it began to be used as a preferred fuel since the 1960s, except for transportation, where oil continues to predominate. In addition, it is also used as the first subject of numerous chemical products. The construction of gas pipelines and natural gas trade has led to major armed conflicts between different countries of the world in the 20th and 21st centuries.
Properties of natural gas
Natural gas is a mixture of gases lighter than water, non-toxic, colorless and in principle odorless. The main component of this fossil fuel is methane (CH4), a simple molecule formed by a carbon atom and four hydrogen atoms, although it also contains other light hydrocarbons such as ethane (C2H6), propane (C3H8), butane (C4H10) or pentane (C5H12) in a much smaller proportion.
The chemical composition of natural gas varies considerably according to its geographical and geological origin. The composition of this non-renewable energy source is usually associated with other molecules or elements such as carbon dioxide (CO2), nitrogen (N2) or rarely helium (He) that must be extracted when natural gas is used for industrial purposes and domestic. In some deposits, for example that of Lacq (France), there may be traces of organic compounds of hydrogen sulfide (SH2) and sulfur-containing organic compounds (bitter finger gases).
To extract the internal energy contained in the chemical bonds C-H, the combustion process must be produced, a thermodynamic reaction. In this way you can take advantage of the fossil fuel energy. The combustion is a thermodynamic reaction of exothermic oxidation of a combustible body (in this case, natural gas) with another oxidizing body (in this case, air) that acts as an oxidizer. This chemical reaction produces a release of heat energy and chemical energy. The phenomenon is usually perceptible by the presence of a flame that also constitutes a source of light.
Origin of natural gas
Natural gas, like other fossil fuels, has been formed for millions of years by the anaerobic decomposition (without oxygen) of large quantities of organismesmorts remains deposited in what had then been the bottom of the sea or a lake. Over time, the organic matter mixed with mud was buried under heavy layers desediments, which subjected it to high pressure and temperature, without air, for a long time, which gradually altered chemically. From this anaerobic decomposition gases were released, especially natural gas.
Today, this non-renewable energy source, natural gas, is often in a gaseous state in bags that are underground near oil bags, which remain in a liquid state. Both fossil fuels are found in rocks of sedimentary origin, where geological phenomena imprison them, one, the other or both, giving rise to large underground pockets. The natural gas may be in the form called dry, that is to say, fully gaseous, or else in a wet form, that is, mixed with longer hydrocarbons, which are easily separated as liquids by compression, refrigeration or absorption.
Dry natural gas is predominantly methane (60% -95%), but may contain appreciable amounts of ethane (5% -20%) depending on the region where it is found.
Last review: August 17, 2016