The explosive limit of natural gas. Physical Properties of Gas

Natural gas is understood to mean a whole mixture of gases that form in the bowels of the earth after anaerobic decomposition of organic substances. It is one of the most important minerals. Natural gas lies in the bowels of the planet. These may be individual clusters or a gas cap in an oil field, but can be represented as gas hydrates, in the crystalline state.

Hazardous properties

Natural gas is familiar to virtually all residents of developed countries, and even at school, children learn the rules of using gas in everyday life. Meanwhile, explosions of natural gas are not uncommon. But besides this, there are a number of threats coming from so convenient appliances that run on natural gas.

Natural gas is toxic. Although ethane and methane are not poisonous in their pure form, when they saturate the air, a person will suffocate because of a lack of oxygen. Especially it is dangerous at night, during sleep.

Explosive limit of natural gas

When exposed to air, or more precisely to its component - oxygen, natural gases are able to form an inflammable detonating mixture that can cause an explosion of great force, even from the slightest source of fire, for example, a spark from the wiring or 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 strength of the explosion depends on the pressure of the resulting mixture: the higher the gas-air composition pressure, the more it will explode.

However, almost all people at least once in their life encountered some leakage of gas, detected by a characteristic odor, and yet no explosions occurred. The thing 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 initiate a combustion reaction, an explosion may occur. Reducing the concentration will eliminate the possibility of a fire. Exceeding the highest mark (15% for methane) also will not allow the burning reaction to start, in view of the lack of air, or rather, oxygen.

The explosive limit of natural gas increases with increasing mixture pressure, and also if the mixture contains inert gases, for example nitrogen.

² до 12 кгс/см ² . 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 combustion

Although at first glance it seems that the explosion and burning are somewhat different things, in fact these processes are the same. The only difference is the intensity of the reaction. During an explosion in a room or any other confined space, the reaction proceeds incredibly quickly. The detonation wave propagates at a rate several times the speed of sound: from 900 to 3000 m / s.

Since methane used in a domestic gas pipeline is natural gas, the volume of oxygen necessary for ignition is also subject to the 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 upper limit) and there is a source of fire.

A stream of gas without an admixture of oxygen, that is, exceeding the maximum limit of ignition, entering the air, will burn with an even flame, the combustion front spreads at a rate of 0.2-2.4 m / s at normal atmospheric pressure.

Properties of gases

Detonation properties are manifested in hydrocarbons of the paraffin series from methane to hexane. The structure of molecules and the molecular weight determine their octane number: detonation properties fall with a decrease in molecular weight, and the octane number increases.

The composition of natural gas includes several hydrocarbons. The first of these is methane (chemical formula CH ₄ ). The physical properties of the gas are: colorless, lighter than air, and odorless. It is quite flammable, but nevertheless it is quite safe in storage, in case if the safety precautions are fully observed. Ethane (C ₂ H ₆ ) also has no color and odor, but is slightly heavier than air. It is combustible, but not used as fuel.

Propane (C ₃ H ₈ ) - a toxic gas without color and odor, is liquefied at low pressure. This useful property allows not only to safely transport propane, but also to isolate 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 everyone

Carbon dioxide (CO ₂ ) is also a part of natural gas. The physical properties of gas know, perhaps, everything: it has no smell, but it is characterized by a sour taste. It is included in a series of gases with the lowest toxicity and is the only (except helium) non-flammable gas in the natural composition.

Helium (He) is a very light gas, the second after hydrogen, colorless and odorless. It is very inert and under normal conditions is not able to react with any substance, it does not participate in the combustion process. Helium is safe, non-toxic, at elevated pressure, along with other inert gases, puts a person in a state of anesthesia.

Hydrogen sulphide (H ₂ S) is a gas without color with a characteristic odor of rotten eggs. Heavy and very poisonous, can cause paralysis of the olfactory nerve, even with a low concentration. 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 for use, but do not include it. Ethylene (C ₂ H ₄ ) - close in properties to ethane, has a pleasant smell and colorless gas. From ethane it is less dense and flammable.

Acetylene (C ₂ H ₂ ) is a colorless explosive gas. It is very flammable, explodes if there is a strong compression. In view of this, acetylene is dangerous to use in everyday life, basically it is used for welding works.

The use of hydrocarbons

As a fuel in household gas appliances, methane is used.

Propane and butane serve as fuel for cars (for example, hybrid vehicles), and in liquefied form they are filled with propane lighters.

But ethane is rarely used as fuel, its main purpose in industry is to obtain ethylene, which is produced on the planet in huge quantities, because it 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 can not be used as fuel, and when storing gas, strict observance of the conditions is necessary.

Although hydrogen sulphide is toxic, in extremely small amounts it is used in medicine. These are so-called hydrogen sulphide baths, whose action is based on the antiseptic properties of hydrogen sulphide.

The main useful property of helium is its small density. This inert gas is used for flights on balloons and airships, they are filled with volatile balloons, popular among children. The ignition of natural gas is impossible: helium does not burn, so you can warm it up without fear of open fire. Hydrogen, adjacent to helium in the periodic table, is even easier, but it is easily ignited. Helium is the only gas that does not have a solid phase under any conditions.

Rules for the use of gas in everyday life

Everyone who uses gas appliances must undergo safety training. The first rule is to monitor the serviceability of devices, periodically check the draft and chimney, if the device provides for the removal of combustion products. After switching off the gas appliance, it is necessary to close the valves and close the valve on the cylinder, if there is one. In the event that the gas supply has suddenly been interrupted, and if there are any faults, you should 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 ventilator for ventilation, then leave the room and call emergency service (telephone 04).

The rules of using gas in everyday life are important to observe, because the slightest malfunction can lead to disastrous consequences.