Methane is a gaseous chemical compound with the chemical formula CH4. This is the simplest representative of alkanes. Other names for this group of organic compounds are: saturated, saturated or paraffinic hydrocarbons. They are characterized by the presence of a simple bond between the carbon atoms in the molecule, and all other valencies of each carbon atom are saturated with hydrogen atoms. For alkanes, the most important reaction is burning. They burn with the formation of gaseous carbon dioxide and water vapor. As a result, a huge amount of chemical energy is released, which is converted into heat or electricity. Methane is a combustible substance and the main component of natural gas, which makes it an attractive fuel. The widespread use of natural resources is based on the methane combustion reaction. Since it is a gas under normal conditions, it is difficult to transport it over long distances from the source; therefore, it is often preliminarily liquefied.
The combustion process consists in the reaction between methane and oxygen, that is, in the oxidation of a simple alkane. The result is carbon dioxide, water and a lot of energy. Combustion of methane can be described by the equation: CH4 [gas] + 2O2 [gas] → CO2 [gas] + 2H2O [steam] + 891 kJ. That is, one methane molecule, when interacting with two oxygen molecules, forms a carbon dioxide molecule and two water molecules. In this case, thermal energy equal to 891 kJ is released. Natural gas is the cleanest fossil fuel for burning, since coal, oil and other types of fuel are more complex in composition. Therefore, during combustion, they release various harmful chemicals into the air. Since natural gas consists mainly of methane (approximately 95%), its by-products practically do not produce by-products or produce much less of them than with other types of fossil fuels.
The calorific value of methane (55.7 kJ / g) is higher than its homologues, for example, ethane (51.9 kJ / g), propane (50.35 kJ / g), butane (49.50 kJ / g) or others types of fuel (wood, coal, kerosene). Combustion of methane gives more energy. To ensure an incandescent bulb with a power of 100 W during a year, it is necessary to burn 260 kg of wood, or 120 kg of coal, or 73.3 kg of kerosene, or only 58 kg of methane, which corresponds to 78.8 m³ of natural gas.
The simplest alkane is an important resource for generating electricity. This happens due to its burning as a fuel of a boiler generating steam, which drives a steam turbine. Also, methane combustion is used to produce hot flue gases, the energy of which ensures the operation of a gas turbine (combustion is carried out to the turbine or in the turbine itself). In many cities, methane is piped into homes for indoor heating and cooking. Compared to other types of hydrocarbon fuels, the combustion of natural gas is characterized by less carbon dioxide and a greater amount of heat generated.
Methane combustion is used to achieve high temperatures in furnaces of various chemical industries, for example, large-capacity ethylene plants. Natural gas mixed with air is fed into the burners of the pyrolysis furnaces. In the process of combustion, flue gases with a high temperature (700-900 ° C) are formed. They heat the pipes (located inside the furnace), into which a mixture of raw materials with water vapor is supplied (to reduce the formation of coke in the pipes of the furnaces). Under the influence of high temperatures, many chemical reactions occur, which result in the target components (ethylene and propylene) and by-products (heavy pyrolysis resin, hydrogen and methane fractions, ethane, propane, C4, C5 hydrocarbons, pyrocondensate; each of them has its own application for example, pyrocondensate is used to produce benzene or gasoline components).
Methane combustion is a complex physicochemical phenomenon based on an exothermic redox reaction, characterized by a high flow rate and the release of a huge amount of heat, as well as heat and mass transfer processes. Therefore, the calculated determination of the combustion temperature of the mixture is a difficult task, since in addition to the composition of the combustible mixture, its pressure and initial temperature strongly influence. With their increase, an increase in the combustion temperature is observed, and heat transfer and mass transfer processes contribute to its decrease. The temperature of methane combustion in the design of processes and apparatuses of chemical production is determined by the calculation method, and in existing plants (for example, in pyrolysis furnaces) it is measured using thermocouples.