In the process of anaerobic (methane or oxygen-free) fermentation in the bowels of the earth, biodegradation of organic substances occurs with the release of free methane (CH4 - the simplest paraffin hydrocarbon). This phenomenon can be described by the reaction equation: organic matter + H2O → CH4 + C5H7NO2 + CO2 + NH4 + H2CO3. As a result, a natural mineral is formed. It lies in layers underground and is in a gaseous or crystalline state (in the form of gas hydrates - methane compounds with water, which are stable at elevated pressures and low temperatures, are in permafrost). In addition, it can be dissolved in water or in oil. The composition of natural gas is not constant and varies from field to field.
The main component of this mineral is methane, its content ranges from 91 to 98%. Heavier paraffin hydrocarbons are also contained : butane (C4H10), propane (C3H8), ethane (C2H6). Inorganic substances are present , which include: hydrogen (H2), nitrogen (N2), carbon dioxide (CO2), hydrogen sulfide (H2S), helium (He), water vapor (H2O). The properties and composition of natural gas, as well as test methods, are regulated by GOST 5542-87. This interstate standard was developed and introduced in the USSR, and is currently valid in several CIS countries. It applies to natural fuels, which are used as fuel and raw materials in industry, as well as fuel in public utilities.
It lies at a depth of one to several kilometers (lower than oil), since it forms at greater pressure and higher temperatures. The depth of its occurrence depends on the deposit, for example, next to Novy Urengoy it is mined at a depth of 6 km. The gas produced through wells from under the ground enters the collection system, and then it is prepared and transported to the consumer. For preparation, a special installation is mounted and launched near the field, which is designed to remove water (interferes with transportation) and sulfur compounds (they are corrosive substances that shorten the life of the equipment and can lead to an emergency). The composition of natural gas is analyzed before and after its drying in absorption columns and purification from hydrogen sulfide.
Helium is also emitted at the plants. In this case, two problems are solved. The first - inert helium (He) reduces the quality characteristics stipulated by GOST 5542-87, for example, the heat of combustion. The second - helium extracted at the low-temperature separation unit is a valuable product in many sectors of the national economy; it is produced in fields with a content of more than 0.1%. The extracted helium is transported under high pressure to consumers in steel cylinders. The qualitative composition of helium, as well as the composition of natural gas, is analyzed for impurities in special chemical laboratories.
The content of hydrocarbon components is analyzed according to GOST 23781-87. According to this regulatory document, the chemical composition of natural gas is determined by chromatographic methods. Helium, hydrogen, nitrogen, oxygen and methane - on a chromatograph with a thermal conductivity detector, in which a chromatographic column with molecular sieves is installed. Hydrocarbons and carbon dioxide - on a chromatograph with a thermal conductivity detector and with a column filled with a spherochrome treated with TEGM ether. The content of components C4-C8 is on a chromatograph with a flame ionization detector and a chromatographic column filled with an inert solid support (chromaton) treated with squalane or dimethyl silicone. Calculate the composition of natural gas in percent volume.
Other characteristics that determine the quality of the product are also examined at different stages of production: from the moment of production to delivery to the consumer. For example, the water content is set at the dew point, GOST 20060-83. Relative density, higher and lower heat of combustion are calculated in accordance with GOST 22667-82 and on the basis of the component composition obtained using chromatographic analysis methods according to GOST 23781-87. To determine hydrogen sulfide (H2S) and mercaptan sulfur (RSH), one of three methods is used (photocalorimetric, potentiometric or iodometric), which is described by GOST 22387.2-97 and is selected depending on the content of the analyzed components. All studies, on the basis of which the composition of natural gas becomes known, are carried out in chemical laboratories, which must meet the requirements of GOST R ISO / IEC 17025-2009.