In the process of anaerobic (methane oroxygen-free) fermentation in the bowels of the earth, biodegradation of organic substances takes place with the liberation of free methane (CH4 - the simplest paraffinic hydrocarbon). This phenomenon can be described by the reaction equation: organic substances + H2O → CH4 + C5H7NO2 + CO2 + NH4 + H2CO3. As a result, a useful natural fossil is formed. It lies in layers underground and is in gaseous or crystalline (in the form of gas hydrates - compounds of methane with water, 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 mineralis methane, its content ranges from 91 to 98%. Also heavier paraffinic hydrocarbons are contained: butane (C4H10), propane (C3H8), ethane (C2H6). There are inorganic substances, 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 currently operates in a number of CIS countries. It applies to natural gas fuels, which are used as fuel and raw materials in industry, and also as a fuel in the municipal economy.
It is located at a depth of one to severalkilometers (lower than oil), since it is formed at higher pressures and higher temperatures. The depth of its occurrence depends on the deposit, for example, near Novy Urengoy it is mined at a depth of 6 km. Extracted, with the help of wells, from the ground gas enters the collection systems, and then it is prepared and transported to the consumer. For preparation near the deposit, a special installation is installed and commissioned, which is designed to remove water (interferes with transportation) and sulfur compounds (they are corrosive substances that shorten the life of equipment and can lead to an emergency situation). The composition of natural gas is analyzed before and after its drying in absorption columns and purification from hydrogen sulphide.
Helium is also emitted in plants.In this case two problems are solved. The first - inert helium (He) reduces the qualitative characteristics provided by GOST 5542-87, for example, the heat of combustion. The second - helium, which is isolated at the low-temperature separation plant, is a valuable product in many branches of the national economy, it is obtained in deposits with a content of more than 0.1%. Extracted helium under great pressure is transported to consumers in steel cylinders. The qualitative composition of helium, as well as the composition of natural gas, is analyzed for the content of impurities in special chemical laboratories.
The content of hydrocarbon components is analyzedaccording to GOST 23781-87. According to this normative 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 spherochrome treated with TEGM ether. The content of C4-C8 components is on a chromatograph with a flame ionization detector and a chromatographic column filled with an inert solid carrier (chromaton) treated with squalane or dimethyl silicone. Calculate the composition of natural gas in percent volumetric.
Also explore other characteristics,Determining the quality of the product, at different stages of production: from the time of extraction to delivery to the consumer. For example, the water content is set according to 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 by chromatographic methods of analysis in accordance with GOST 23781-87. To determine hydrogen sulfide (H2S) and mercaptan sulfur (RSH), one of three methods is used (colorimetric, potentiometric or iodometric), which describes 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, is carried out in chemical laboratories that must meet the requirements of GOST R ISO / IEC 17025-2009.
