Combustion of methane

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 the remaining valencies of each carbon atom are saturated with hydrogen atoms. For alkanes, the most important reaction is combustion. They burn with the formation of gaseous carbon dioxide and water vapor. As a result, a huge amount of chemical energy is released, which turns into heat or electricity. Methane is a combustible substance and a major component of natural gas, which makes it an attractive fuel. The wide use of natural fossil is based on the reaction of burning methane. Since it under normal conditions is a gas, it is difficult to transport it to distant distances from the source, so it is often previously liquefied.

The combustion process consists in the reaction between methane and oxygen, that is, in the oxidation of the simplest alkane. As a result, carbon dioxide, water and a lot of energy are formed. Combustion of methane can be described by the equation: CH4 [gas] + 2O2 [gas] → CO2 [gas] + 2H2O [vapor] + 891 kJ. That is, one molecule of methane when interacting with two oxygen molecules forms a molecule of carbon dioxide and two molecules of water. In this case, the heat energy is equal to 891 kJ. Natural gas is the cleanest for burning fossils, since coal, oil and other fuels are more complex in composition. Therefore, during combustion, they release various harmful chemicals into the air. Since natural gas mainly consists of methane (about 95%), its combustion produces little or no by-products, or is much less than in the case of other 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 other Types of fuel (wood, coal, kerosene). Burning methane gives more energy. To ensure that a 100-watt incandescent bulb burns 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 is due to burning it as a boiler fuel producing steam that drives a steam turbine. Also, the combustion of methane is used to produce hot flue gases, the energy of which ensures the operation of the gas turbine (combustion is carried out to the turbine or in the turbine itself). In many cities, methane is fed through pipes to houses for internal heating and cooking. Compared with other types of hydrocarbon fuels, natural gas combustion is characterized by a lower carbon dioxide emission and a greater amount of heat produced.

Combustion of methane 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 pyrolysis furnaces. During combustion, flue gases with a high temperature (700-900 ° C) are formed. They heat the pipes (they are inside the furnace) into which a mixture of raw materials with water vapor is fed (to reduce the formation of coke in the furnace pipes). Under the influence of high temperatures, a lot of chemical reactions take place, resulting in the production of the target components (ethylene and propylene) and by-products (pyrolysis heavy, hydro and methane fractions, ethane, propane, C4, C5, pyrocondensate, each of which has its application , For example, pyrocondensate is used to produce benzene or components of motor gasoline).

Combustion of methane is a complex physico-chemical phenomenon based on an exothermic oxidation-reduction reaction, characterized by a high flow rate and the release of a huge amount of heat, as well as by heat exchange and mass-transfer processes. Therefore, the calculated determination of the combustion temperature of the mixture is a complex task, since in addition to the composition of the combustible mixture, its pressure and initial temperature are strongly influenced. With their increase, the burning temperature is observed, and heat exchange and mass-exchange processes contribute to its decrease. The combustion temperature of methane in the design of processes and apparatuses of chemical production is determined by the calculation method, and at operating installations (for example, in pyrolysis furnaces), it is measured with thermocouples.