Natural gas in an energy product, whose use is growing fast since it is the most energetically efficient and ecologically by far most appropriate of the fossil fuels.
Natural gas was created many millions of years ago. The flora and fauna, which the rocky masses buried in the seas and lakes, transformed due to high pressure and great heat into hydrocarbons of various states – solid (coals), liquid (petroleum) and gaseous (natural gas). According to a different explanation, natural gas is still being created in processes, which take place in the great depths of the Earth. It comes closer to the surface during earthquakes and movements of earth’s layers.
Natural gas is a mixture of various gases with a majority of methane (even up to 99%). Ethane, propane, butane, mixtures of heavier hydrocarbons, nitrogen and carbon dioxide are all present in smaller quantities.
Combustion of natural gas
Natural gas is located even up to 5 and more thousand metres below the earth’s surface in the porous earth layers beneath the impermeable earth layers. It is under pressure, which may be greater than 300 bars, depending on the depth of gas well, and has a temperature which can exceed 180 °C. Most commonly, it is in the form of a gas deposits above petroleum in oil fields and enables extraction of crude oil without pumping. Underground natural gas fields without the presence of petroleum are also common (pure gas fields).
Natural gas is colourless and odourless. For safety reasons it is added an odorant for general consumption so that people are able to detect it already in a concentration, which is far below than the min. level of explosivity.
Most commonly, it is measured in Sm3 (standard cubic metre is a quantity of gas, which at pressure of 1013.25 mbar and temperature of 15°C has a volume of 1 m3).
Natural gas is lighter than air (density of air is 1.293 kg/Sm3, density of natural gas is 0.68 kg/Sm3); consequently it rises quickly in air.
It ignites at a temperature between 595 and 630 °C. Its boiling point is at -161 °C, while it freezes at -182 °C.
Natural gas sold in Slovenia has a rated heating value (»lower calorific power«) of 34.1 MJ/Sm3.
Natural gas burns with a characteristic blue flame. Its combustion releases heat and creates carbon dioxide and water vapour. In a mixture with air it is explosive in a ratio of 5 to 16% of natural gas in the air. Greater explosions occur with concentrations near the lower limit.
We transport it in gaseous state through gas pipelines or in liquid state by special LNG carriers for liquid natural gas, rarely by railways and vehicular transport in thermally insulated cisterns.
We use it for heating, cooling, heat production in technological processes, electricity production and as a raw material of a wide range in the chemical industry.
Liquefied petroleum gas
It is important to distinguish between natural gas and liquefied petroleum gas (LPG, sometimes referred to as propane-butane). Liquefied petroleum gas is a product of crude oil processing. We generally keep it in cylinders and gasholder works. Liquefied petroleum gas is heavier than air, consequently the spaces where it is used must be thoroughly aired, while natural gas is lighter than air and quickly dissipates upon possible leak.