Natural gas is understood to mean a whole mixture of gases that are formed in the bowels of the earth afterwards anaerobic decomposition of organic substances. It is one of the most important minerals. Natural gas lies in the bowels of the planet. It can be separate accumulations or a gas cap in an oil field, however it can be presented in the form of gas hydrates, in a crystalline state.
Hazardous properties
Natural gas is familiar to almost all residents of developed countries, and even at school, children learn the rules of using gas in everyday life. Meanwhile, natural gas explosions are not uncommon. But besides this, there are a number of threats posed by such convenient devices that run on natural gas.
Natural gas is toxic. Although ethane and methane in their pure form are non-toxic, when saturated with air, a person will suffocate due to a lack of oxygen. This is especially dangerous at night, during sleep.
Explosion limit of natural gas
When in contact with air, or rather its component, oxygen, natural gases can form a flammable detonating mixture, which can cause a large explosion even from the smallest source of fire, for example, a spark from a wiring or a flame of a match, a candle. If the mass of natural gas is relatively low, then the ignition temperature will not be high, but the force of the explosion depends on the pressure of the resulting mixture: the higher the pressure of the gas-air composition, the more it will explode.
However, almost all people at least once in their life encountered a gas leak detected by a characteristic odor, and yet no explosions occurred. The fact is that natural gas can explode only when certain proportions with oxygen are reached. There is a lower and higher explosive limit.
As soon as the lowest explosive limit of natural gas is reached (for methane it is 5%), that is, a concentration sufficient to start the combustion reaction, an explosion can occur. Reduced concentration will eliminate the possibility of fire. Exceeding the highest level (15% for methane) will also not allow the combustion reaction to begin, due to a lack of air, or rather, oxygen.
The explosive limit of natural gas increases with increasing pressure of the mixture, as well as if the mixture contains inert gases, such as nitrogen.
The pressure of natural gas in the gas pipeline can be different, from 0.05 kgf / cm 2 to 12 kgf / cm 2 .
The difference between explosion and burning
Although at first glance it seems that explosion and combustion are somewhat different things, in fact, these processes are of the same type. Their only difference is the intensity of the reaction. During an explosion in a room or any other enclosed space, the reaction proceeds incredibly quickly. The detonation wave propagates at a speed several times higher than the speed of sound: from 900 to 3000 m / s.
Since the methane used in the domestic gas pipeline is natural gas, the amount of oxygen needed for ignition also follows a general rule.
The maximum explosion force is achieved if the oxygen present is theoretically sufficient for complete combustion. Other conditions must also be present: the gas concentration corresponds to the ignition limit (above the lower limit, but below the highest) and a source of fire is present.
A gas jet without oxygen impurity, that is, exceeding the highest ignition limit, entering the air will burn with an even flame, the combustion front propagates at a speed of 0.2-2.4 m / s at normal atmospheric pressure.
Gas properties
Detonation properties are manifested in hydrocarbons of the paraffin series from methane to hexane. The structure of molecules and molecular mass determine their octane number: detonation properties decrease with decreasing molecular weight, and the octane number increases.
Natural gas contains several hydrocarbons. The first of these is methane (chemical formula CH 4 ). The physical properties of the gas are as follows: colorless, lighter than air and odorless. It is quite combustible, but nevertheless quite safe to store, in case the safety measures are fully observed. Ethane (C 2 H 6 ) is also colorless and odorless, but slightly heavier than air. It is combustible but not used as fuel.
Propane (C 3 H 8 ) is a poisonous gas without color and odor, capable of liquefying at low pressure. This useful property allows not only to safely transport propane, but also to separate it from a mixture with other hydrocarbons.
Butane (C 4 H 10 ): The physical properties of the gas are close to propane, but its density is higher and the mass of butane is twice as heavy as air.
Familiar to all
Carbon dioxide (CO 2 ) is also part of natural. Perhaps everyone knows the physical properties of the gas: it has no smell, but is characterized by a sour taste. It is one of the gases with the smallest toxicity and is the only (except helium) non-combustible gas in natural gas.
Helium (He) is a very light gas, the second after hydrogen, is colorless and odorless. It is very inert and under normal conditions is not able to react with any substance, does not participate in the combustion process. Helium is safe, non-toxic, with elevated pressure, along with other inert gases, it introduces a person into a state of anesthesia.
Hydrogen sulfide (H 2 S) is a colorless gas with a characteristic smell of rotten eggs. Severe and very poisonous, can cause paralysis of the olfactory nerve even at low concentrations. In addition, the explosive limit of natural gas is very wide, from 4.5% to 45%.
Similar gases
There are two more hydrocarbons that are close to natural gas in use, but are not part of it. Ethylene (C 2 H 4 ) is close in its properties to ethane, which has a pleasant smell and colorless gas. It is distinguished from ethane by lower density and combustibility.
Acetylene (C 2 H 2 ) is a colorless explosive gas. It is very combustible, explodes if severe compression has occurred. In view of this, acetylene is dangerous to use in everyday life, but it is mainly used in welding work.
The use of hydrocarbons
As fuel in household gas appliances, methane is used.
Propane and butane serve as fuel for automobiles (for example, hybrid ones), and lighters are charged with propane in a liquefied form.
But ethane is rarely used as fuel, its main purpose in industry is to produce ethylene, which is produced on the planet in huge quantities, because it is it that is the raw material for polyethylene.
Acetylene serves the needs of metallurgy, with its help high temperatures are achieved for welding and cutting metals. Since it is extremely flammable, it cannot be used as fuel, and when storing gas, strict adherence to conditions is necessary.
Although hydrogen sulfide is toxic, in extremely small quantities it is used in medicine. These are the so-called hydrogen sulfide baths, the action of which is based on the antiseptic properties of hydrogen sulfide.
The main useful property of helium is its low density. This inert gas is used when flying on balloons and airships, it is filled with flying balloons, popular among children. Ignition of natural gas is impossible: helium does not burn, so you can heat it over open fire without fear. Hydrogen adjacent to helium in the periodic table is even lighter, but easily ignited. Helium is the only gas that does not have a solid phase under any conditions.
Household gas regulations
Every person who uses gas appliances is required to undergo safety training. The first rule is to monitor the serviceability of the devices, periodically check the draft and chimney, if the device provides for the removal of combustion products. After turning off the gas appliance, it is necessary to close the taps and close the valve on the cylinder, if any. In the event that the gas supply is suddenly interrupted, as well as in the event of a malfunction, call the gas service immediately.
If the smell of gas is felt in an apartment or other room, it is necessary to immediately stop any use of appliances, do not turn on electrical appliances, open a window or window for ventilation, then leave the room and call the emergency service (telephone 04).
The rules for using gas in everyday life are important to observe, because the slightest malfunction can lead to disastrous consequences.