Combustible gases are substances with a low threshold of calorific value. This is the main component of gaseous fuel, which is used for gas supply to cities, in industry and other spheres of life. Physico-chemical characteristics of such gases depend on the presence of non-combustible components and harmful impurities in their composition.
Types and origin of combustible gases
Combustible gases contain methane, propane, butane, ethane, hydrogen and carbon monoxide, sometimes with impurities of hexane and pentane. They are obtained in two ways - from natural deposits and artificially. Gases of natural origin - fuel, the result of a natural biochemical process of decomposition of organics. Most deposits are located at a depth of less than 1.5 km and consist mainly of methane with small admixtures of propane, butane and ethane. With increasing depth, the percentage of impurities increases. It is extracted from natural deposits or as associated gases from oil fields.
Most often, natural gas deposits are concentrated in sedimentary rocks (sandstones, pebbles). The dense clay rocks serve as covering and underlying layers. The sole is mainly oil and water. Artificial - combustible gases obtained as a result of thermal processing of various types of solid fuels (coke, etc.) and derivatives of oil refining.
The main component of natural gases produced in dry deposits is methane with a small amount of propane, butane and ethane. Natural gas is characterized by a constant composition, belongs to the category of dry. The gas composition obtained during refining and from mixed gas and oil deposits is variable and depends on the magnitude of the gas factor, the nature of the oil and the conditions for the separation of oil and gas mixtures. It includes a significant amount of propane, butane, ethane, as well as other light and heavy hydrocarbons contained in oil, up to kerosene and gasoline fractions.
The extraction of combustible natural gases consists in extracting it from the bowels of the earth, collecting, removing excess moisture and preparing for transportation to the consumer. The peculiarity of gas production is that at all stages from the reservoir to the end user, the entire process is sealed.
Combustible gases and their properties
Heat production - the maximum temperature emitted during the complete combustion of dry gas in the theoretically necessary amount of air. In this case, the heat generated is spent on heating the combustion products. For methane, this parameter in ° C is 2043, butane - 2118, propane - 2110.
Ignition temperature - the lowest temperature at which a spontaneous ignition process occurs without exposure to an external source, spark or flame, due to the heat released by the gas particles. This parameter is especially important for determining the permissible surface temperature of devices used in hazardous areas, which should not exceed the ignition temperature. For such equipment, a temperature class is assigned.
Flash point - the lowest temperature at which enough vapor is emitted (on the surface of a liquid) to ignite from the smallest flame. This property should not be generalized with the ignition temperature, since these parameters can vary significantly.
Gas / vapor density. It is determined in comparison with air, whose density is 1. The gas density <1 - increases,> 1 - decreases. For example, for methane, this figure is 0.55.
Flammable gas hazard
Combustible gases present a hazard with three of their properties:
- Combustibility There is a risk of fire associated with uncontrolled gas ignition;
- Toxicity. The risk of poisoning by gas or its combustion products (carbon monoxide);
- Choking due to oxygen deficiency, which may be replaced by another gas.
The combustion process is a chemical reaction that involves oxygen. In this case, energy is released in the form of heat, flame. The igniter is gas. The gas combustion process is possible in the presence of three factors:
- Ignition source.
- Flammable gases.
- Oxygen.
The purpose of fire protection is to eliminate at least one of the factors.
Methane
It is a colorless, light, odorless flammable gas. Non toxic Methane makes up 98% of all natural gases. It is considered the main determining property of natural gas. 75% carbon and 25% hydrogen. Mass cube meters - 0.717 kg. It liquefies at a temperature of 111 K, while its volume decreases by 600 times. It has a low reactivity.
Propane
Propane gas is a flammable gas, without color and odor. It has a greater reactivity than methane. The content in natural gas is 0.1-11% by weight. In associated gases from mixed gas and oil fields up to 20%, in products of processing solid fuels (brown and hard coal, coal tar) up to 80%. Propane gas is used in various reactions to produce ethylene, propylene, lower olefins, lower alcohols, acetone, formic and propionic acid, nitroparaffins.
Butane
Flammable gas without color, with a peculiar smell. Butane gas is easily compressible and volatile. Contained in oil gas up to 12% by volume. Also obtained as a result of cracking of oil fractions and laboratory tests according to the Wurz reaction. The freezing temperature is -138 . Like all hydrocarbon gases, it is flammable. Harmful to the nervous system; if inhaled, causes respiratory dysfunction. Butane (gas) has narcotic properties.
Ethane
Ethane is a gas without color and odor. Representative of hydrocarbons. Dehydrogenation at 550-650 0 leads to ethylene, more than 800 0 - to acetylene. Contained in natural and associated gases up to 10%. It is distinguished by low-temperature distillation. Significant amounts of ethane are released during oil cracking. In laboratory conditions obtained by the Wurz reaction. It is the main raw material for vinyl chloride and ethylene.
Hydrogen
Odorless transparent gas. Non-toxic, 14.5 times lighter than air. In appearance, hydrogen does not differ from air. It has high reactivity, wide ignition limits, and is highly explosive. It is part of almost all organic compounds. The most difficult to compress gas. Free hydrogen is extremely rare in nature, but in the form of compounds is very common.
Carbon monoxide
Colorless gas, without taste and odor. Weight is 1 cubic m - 1.25 kg. It is contained in high-calorie gases along with methane and other hydrocarbons. An increase in the proportion of carbon monoxide in a combustible gas lowers the calorific value. It has a toxic effect on the human body.
Use of flammable gases
Combustible gases have a high calorific value, and therefore are highly economical energy fuels. They are widely used for household needs, in power plants, in metallurgy, glass, cement and food industry, as automobile fuel, in the production of building materials.
The use of combustible gases as raw materials for the production of organic compounds such as formaldehyde, methyl alcohol, acetic acid, acetone, acetaldehyde is due to the presence of hydrocarbons in their composition. Methane, as the main component of combustible natural gases, is widely used for the production of various organic products. To obtain ammonia and various kinds of alcohols, synthesis gas is used - the product of the conversion of methane by oxygen or water vapor. Pyrolysis and dehydrogenation of methane produce acetylene, along with hydrogen and soot. Hydrogen, in turn, is used to synthesize ammonia. Combustible gases, primarily ethane, are used in the production of ethylene and propylene, which are subsequently used as raw materials for the production of plastics, artificial fibers and synthetic rubbers.
A promising type of fuel for many sectors of the economy is liquefied methane. The use of liquefied gases in many cases provides great economic benefits, making it possible to reduce material costs for transportation and solving gas supply problems in certain areas, and creating reserves of raw materials for the needs of the chemical industry.