The use of natural gas. Natural gas: composition, properties

Definition
Natural gas is a mineral in the gaseous state. It is widely used as a fuel. But natural gas itself is not used as a fuel, its components are separated from it for separate use.

Composition of natural gas
Up to 98% of natural gas is methane, it also includes methane homologues - ethane, propane and butane. Sometimes carbon dioxide, hydrogen sulfide and helium may be present. This is the composition of natural gas.

Physical Properties
Natural gas is colorless and odorless (if it does not contain hydrogen sulfide), it is lighter than air. Flammable and explosive.
Below are more detailed properties of natural gas components.

Properties of individual constituents of natural gas (consider the detailed composition of natural gas)

Methane(CH4) is a colorless, odorless gas, lighter than air. Flammable, but still it can be stored with sufficient ease.

Ethane(C2H6) is a colorless, odorless and colorless gas, slightly heavier than air. Also combustible, but not used as a fuel.

Propane(C3H8) is a colorless, odorless gas, poisonous. It has a useful property: propane liquefies at low pressure, which makes it easy to separate it from impurities and transport it.

Butane(C4H10) - similar in properties to propane, but has a higher density. Twice as heavy as air.

Carbon dioxide(CO2) is a colorless, odorless gas with a sour taste. Unlike the other components of natural gas (with the exception of helium), carbon dioxide does not burn. Carbon dioxide is one of the least toxic gases.

Helium(He) - colorless, very light (the second of the lightest gases, after hydrogen) without color and odor. Extremely inert, under normal conditions does not react with any of the substances. Does not burn. It is not toxic, but at elevated pressure it can cause anesthesia, like other inert gases.

hydrogen sulfide(H2S) is a colorless heavy gas with a smell of rotten eggs. Very poisonous, even at very low concentrations it causes paralysis of the olfactory nerve.
Properties of certain other gases that are not part of natural gas but have uses similar to those of natural gas

Ethylene(C2H4) - A colorless gas with a pleasant smell. It is similar in properties to ethane, but differs from it in lower density and flammability.

Acetylene(C2H2) is an extremely flammable and explosive colorless gas. With strong compression, it can explode. It is not used in everyday life due to the very high risk of fire or explosion. The main application is in welding work.

Application

Methane used as fuel in gas stoves.

propane and butane as fuel in some vehicles. Lighters are also filled with liquefied propane.

Ethane it is rarely used as a fuel, its main use is the production of ethylene.

Ethylene is one of the most produced organic substances in the world. It is a raw material for the production of polyethylene.

Acetylene used to create a very high temperature in metallurgy (reconciliation and cutting of metals). Acetylene it is very combustible, therefore it is not used as a fuel in cars, and even without this, the conditions for its storage must be strictly observed.

hydrogen sulfide, despite its toxicity, is used in small quantities in the so-called. sulfide baths. They use some of the antiseptic properties of hydrogen sulfide.

The main useful property helium is its very low density (7 times lighter than air). Helium fill balloons and airships. Hydrogen is even lighter than helium, but at the same time combustible. Helium balloons are very popular among children.

Toxicity

Carbon dioxide. Even large amounts of carbon dioxide do not affect human health in any way. However, it prevents the absorption of oxygen when the content in the atmosphere is from 3% to 10% by volume. At this concentration, suffocation and even death begin.

Helium. Helium is completely non-toxic under normal conditions due to its inertness. But with increased pressure, the initial stage of anesthesia occurs, similar to the effect of laughing gas *.

hydrogen sulfide. The toxic properties of this gas are great. With prolonged exposure to the sense of smell, dizziness and vomiting occur. The olfactory nerve is also paralyzed, so there is an illusion of the absence of hydrogen sulfide, but in fact the body simply does not feel it anymore. Hydrogen sulfide poisoning occurs at a concentration of 0.2-0.3 mg / m3, a concentration above 1 mg / m3 is fatal.

combustion process
All hydrocarbons, when fully oxidized (excess oxygen), release carbon dioxide and water. For example:
CH4 + 3O2 = CO2 + 2H2O
With incomplete (lack of oxygen) - carbon monoxide and water:
2CH4 + 6O2 = 2CO + 4H2O
With an even smaller amount of oxygen, finely dispersed carbon (soot) is released:
CH4 + O2 = C + 2H2O.
Methane burns with a blue flame, ethane - almost colorless, like alcohol, propane and butane - yellow, ethylene - luminous, carbon monoxide - light blue. Acetylene - yellowish, strongly smokes. If you have a gas stove at home and instead of the usual blue flame you see yellow, you should know that methane is diluted with propane.

Notes

Helium, unlike any other gas, does not exist in a solid state.
Laughing gas is the trivial name for nitrous oxide N2O.

Comments and additions to the article - in the comments.

Natural gas, the main part of which is methane (92-98%), is by far the most promising alternative fuel for cars. Natural gas can be used as fuel both in compressed (compressed) and liquefied form.

Methane- the simplest hydrocarbon, a colorless gas (under normal conditions) odorless, the chemical formula is CH4. Slightly soluble in water, lighter than air. When used in everyday life, industry, odorants (usually thiols) with a specific "gas smell" are usually added to methane. Methane is non-toxic and harmless to human health.

Extraction and transportation

The gas is located in the bowels of the Earth at a depth of one to several kilometers. Before the start of gas production, it is necessary to carry out geological exploration work, which allows to establish the location of deposits. Gas is produced using wells specially drilled for this purpose in one of the possible ways. Most often, gas is transported through gas pipelines. The total length of gas distribution pipelines in Russia is more than 632 thousand kilometers - this distance is almost 20 times the circumference of the Earth. The length of main gas pipelines in Russia is 162,000 kilometers.

Use of natural gas

The scope of natural gas is quite wide: it is used for space heating, cooking, heating water, the production of paints, glue, acetic acid and fertilizers. In addition, natural gas in compressed or liquefied form can be used as a motor fuel in vehicles, special and agricultural machinery, railway and water transport.

Natural gas - environmentally friendly motor fuel

90% of air pollution comes from vehicles.

Transfer of transport to environmentally friendly motor fuel - natural gas - allows to reduce emissions of soot, highly toxic aromatic hydrocarbons, carbon monoxide, unsaturated hydrocarbons and nitrogen oxides into the atmosphere.

When burning 1000 liters of liquid petroleum motor fuel, 180-300 kg of carbon monoxide, 20-40 kg of hydrocarbons, 25-45 kg of nitrogen oxides are emitted into the air together with exhaust gases. When natural gas is used instead of petroleum fuel, the release of toxic substances into the environment is reduced by approximately 2-3 times for carbon monoxide, for nitrogen oxides - 2 times, for hydrocarbons - 3 times, for smoke - 9 times, and the formation of soot, characteristic of diesel engines is absent.

Natural gas - economical motor fuel

Natural gas is the most economical motor fuel. Its processing requires minimal costs. In fact, all that needs to be done with gas before refueling a car is to compress it in a compressor. Today, the average retail price of 1 cubic meter of methane (which in terms of its energy properties is equal to 1 liter of gasoline) is 13 rubles. This is 2-3 times cheaper than gasoline or diesel fuel.

Natural gas is a safe motor fuel

The concentration* and temperature** flammability limits of natural gas are significantly higher than those of gasoline and diesel fuel. Methane is twice as light as air and quickly dissolves into the atmosphere when released.

According to the “Classification of combustible substances according to the degree of sensitivity” of the Ministry of Emergency Situations of Russia, compressed natural gas is classified as the safest, fourth class, and propane-butane - to the second.

* The formation of an explosive concentration occurs when the content of gas vapor in the air is from 5% to 15%. In open space, the formation of an explosive mixture does not occur.
** The lower self-ignition limit of methane is 650°C.

Natural gas - technologically advanced motor fuel

Natural gas does not form deposits in the fuel system, does not wash off the oil film from the cylinder walls, thereby reducing friction and reducing
engine wear.

The combustion of natural gas does not produce solid particles and ash, which cause increased wear of engine cylinders and pistons

Thus, the use of natural gas as a motor fuel makes it possible to increase the service life of the engine by 1.5-2 times.

The table below summarizes a few facts about CNG and LNG:

There is a mixture of methane CH 4 with a small amount of nitrogen N 2 and carbon dioxide CO 2 - that is, that it is qualitatively identical in composition with the gas emitted from swamps.

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Chemical composition

The main part of natural gas is methane (CH 4) - from 70 to 98%. The composition of natural gas may include heavier hydrocarbons - methane homologues:

• ethane (C 2 H 6),
• propane (C 3 H 8),
• butane (C 4 H 10).

Natural gas also contains other substances that are not hydrocarbons:

• helium (He) and other inert gases.

Pure natural gas is colorless and odorless. To facilitate the possibility of determining a gas leak, odorants are added to it in a small amount - substances that have a sharp unpleasant odor (rotten cabbage, rotten hay, rotten eggs). The most commonly used odorants are thiols (mercaptans), such as ethyl mercaptan (16 g per 1000 m³ of natural gas).

Physical Properties

Approximate physical characteristics (depending on the composition; under normal conditions, unless otherwise indicated):

Natural gas fields

Huge deposits of natural gas are concentrated in the sedimentary shell of the earth's crust. According to the theory of the biogenic (organic) origin of oil, they are formed as a result of the decomposition of the remains of living organisms. It is believed that natural gas is formed in the sedimentary shell at higher temperatures and pressures than oil. Consistent with this is the fact that gas fields are often deeper than oil fields.

Huge reserves of natural gas are possessed by Russia (Urengoyskoye field), Iran, most of the countries of the Persian Gulf, the USA, Canada. Of the European countries, it is worth noting Norway, the Netherlands. Among the former republics of the Soviet Union, Turkmenistan, Azerbaijan, Uzbekistan, and Kazakhstan (Karachaganak field) own large gas reserves.

Methane and some other hydrocarbons are widely distributed in space. Methane is the third most abundant gas in the universe, after hydrogen and helium. In the form of methane ice, it is involved in the structure of many planets and asteroids distant from the sun, but such accumulations, as a rule, are not classified as natural gas deposits, and they have not yet found practical application. A significant amount of hydrocarbons is present in the Earth's mantle, but they are also of no interest.

Gas hydrates

In science, it has long been believed that accumulations of hydrocarbons with a molecular weight of more than 60 are in the earth's crust in a liquid state, while lighter ones are in a gaseous state. However, in the second half of the 20th century, a group of researchers A. A. Trofimuk, N. V. Chersky, F. A. Trebin, Yu. solid state and form gas hydrate deposits. Later it turned out that the reserves of natural gas in this state are huge.

The gas passes into a solid state in the earth's crust, connecting with formation water at hydrostatic pressures up to 250 atm and relatively low temperatures (up to +22 °C). Gas hydrate deposits have an incomparably higher concentration of gas per unit volume of the porous medium than in ordinary gas deposits, since one volume of water, when it passes into the hydrate state, binds up to 220 volumes of gas. The zones of gas hydrate deposits are concentrated mainly in the areas of permafrost, as well as at a shallow depth under the ocean floor.

Natural gas reserves

Extraction and transportation

Natural gas is found in the ground at depths ranging from 1,000 m to several kilometers. An ultra-deep well near the city of Novy Urengoy received gas inflow from a depth of more than 6,000 meters. In the bowels of the gas is in microscopic voids (pores). The pores are interconnected by microscopic channels - cracks, through these channels the gas flows from the pores with high pressure to the pores with lower pressure until it reaches the well. The movement of gas in a reservoir obeys certain laws.

Gas is extracted from the bowels of the earth with the help of wells. Wells are trying to be placed evenly throughout the field, for a uniform drop in reservoir pressure in the deposit. Otherwise, gas flows between areas of the deposit are possible, as well as premature flooding of the deposit.

Gas comes out of the bowels due to the fact that in the reservoir it is under pressure many times higher than atmospheric pressure. Thus, the driving force is the pressure difference between the reservoir and the collection system.

World natural gas production in 2014 amounted to 3460.6 bcm. The leading position in gas production is occupied by Russia and the United States.

Preparation of natural gas for transportation

The gas coming from the wells must be prepared for transportation to the end user - a chemical plant, boiler room, CHP, city gas networks. The need for gas preparation is caused by the presence in it, in addition to the target components (different components are targeted for different consumers), also impurities that cause difficulties during transportation or use. So, water vapor contained in gas, under certain conditions, can form hydrates or, condensing, accumulate in various places (for example, a bend in a pipeline), interfering with the movement of gas; hydrogen sulfide causes severe corrosion of gas equipment (pipes, heat exchanger tanks, etc.). In addition to preparing the gas itself, it is also necessary to prepare the pipeline. Nitrogen plants are widely used here, which are used to create an inert atmosphere in the pipeline.

Gas is prepared according to various schemes. According to one of them, in the immediate vicinity of the field, a complex gas treatment unit (CGTP) is being built, where gas is cleaned and dried in absorption columns. Such a scheme has been implemented at the Urengoyskoye field. Gas treatment by membrane technology is also expedient.

To prepare gas for transportation, technological solutions are used using membrane gas separation, which can be used to separate heavy hydrocarbons (C 3 H 8 and above), nitrogen, carbon dioxide, hydrogen sulfide, and also significantly reduce the dew point temperature for water and hydrocarbons before being fed into GTS.

If the gas contains a large amount of helium or hydrogen sulfide, then the gas is processed at a gas processing plant, where sulfur is isolated at amine treatment plants and Claus plants, and helium at cryogenic helium plants (CGU). This scheme has been implemented, for example, at the Orenburg field. If the hydrogen sulfide content in the gas is less than 1.5% by volume, then it is also advisable to consider the membrane technology for natural gas treatment, since its use allows reducing capital and operating costs by 1.5-5

The dead living organisms sank to the bottom of the sea and fell into such conditions where they could not decay either as a result of oxidation (there is practically no air and oxygen at the bottom of the sea), or under the action. As a result, these organisms formed silty sediments.

Under the influence of geological movements, these sediments descended to ever greater depths, penetrating into the bowels of the earth. For millions of years, sediments have been subjected to high pressures and temperatures. As a result of this impact, a process took place in these sediments, in which the carbon contained in them passed into compounds called hydrocarbons.

High molecular weight hydrocarbons (with large molecules) are liquid substances. From them, oil was formed. But low molecular weight hydrocarbons are gases. From the latter, natural gas is formed. Only the formation of gas requires higher temperatures and pressures. Therefore, there is always natural gas in the oil field.

Over time, deposits of oil and gas have gone to great depths. For millions of years they were blocked by sedimentary rocks.

Natural gas is a mixture of gases, not a homogeneous substance. The main part of this mixture, about 98%, is methane gas. In addition to methane, natural gas contains ethane, propane, butane and a few non-hydrocarbon elements - hydrogen, nitrogen, carbon dioxide, hydrogen sulfide.

Where is natural gas located

Natural gas is located in the bowels of the earth at a depth of about 1000 m and deeper. There it fills microscopic voids - pores that are interconnected by cracks. Through these cracks, the gas in the earth can move from high-pressure pores to low-pressure pores.

Also, gas can be located in the form of a gas cap above the oil field. In addition, it can also be in a dissolved state - in oil or water. Pure natural gas is colorless and odorless.

Production and transportation of gas

Gas is extracted from the ground using wells. Due to the fact that at a depth the pressure is greater, the gas escapes from the wells through the pipe.

To facilitate transportation and storage, natural gas is liquefied by exposure to low temperatures at elevated pressures. Methane and ethane cannot exist in a liquid state, so the gas is separated. As a result, only a mixture of propane and heavier hydrocarbons is transported in cylinders.

Burning natural gas

Natural gas is a mineral in the gaseous state. It is used very widely as a fuel. But natural gas itself is not used as a fuel, its components are separated from it for separate use. It is often associated gas in oil production. Natural gas in reservoir conditions (conditions of occurrence in the earth's interior) is in a gaseous state in the form of separate accumulations (gas deposits) or in the form of a gas cap of oil and gas fields - this is free gas; or in a dissolved state in oil or water (in reservoir conditions), and under standard conditions - only in a gaseous state. Natural gas can also be in the form of gas hydrates.

Almost 90% it consists of hydrocarbons, mainly methane (CH 4). It also contains heavier hydrocarbons - ethane, propane, butane, as well as mercaptans and hydrogen sulfide (usually these impurities are harmful), nitrogen and carbon dioxide (they are basically useless, but not harmful), water vapor, useful impurities of helium and other inert gases.

Chemical composition

The main part of natural gas is methane (CH 4) - up to 98%. The composition of natural gas may also include heavier hydrocarbons - methane homologues:

• ethane (C 2 H 6),
• propane (C 3 H 8),
• butane (C 4 H 10),
• and other alkanes - from C 5 and above

As well as other non-hydrocarbon substances:

• a more thorough analysis made it possible to detect small amounts of helium (He) in natural gas.

Physical Properties

Approximate physical characteristics (depending on the composition):

• Density :
  • from 0.7 to 1.0 kg / m 3 - dry gaseous, at n. y.
  • 400 kg / m 3 - liquid.
• The heat of combustion of one m 3 of natural gas in the gaseous state at n.o.: 28-46 MJ, or 6.7-11.0 Mcal.
• Octane number when used in internal combustion engines: 120-130.
• The concentration limits of ignition (explosion) of natural gas (methane) are in the range from 5 to 15%. Outside these limits, the gas-air mixture is not capable of flame propagation. During an explosion, the pressure in a closed volume rises to 0.8 ... 1 MPa.
• Pure natural gas is colorless and odorless. In order to be able to determine the leak by smell, a small amount of odorants (most often ethyl mercaptan is used as an odorant), which have a strong unpleasant odor, are added to the gas, these are odorants.
• Natural gas quickly escapes and dissipates in the atmosphere, which is important from a safety point of view.

Natural gas reserves

Map of natural gas reserves in the world

Methane and some other hydrocarbons are widely distributed in space. Methane- the third most common gas in the universe, after hydrogen and helium. In the form of methane ice, it is involved in the structure of many planets and asteroids distant from the sun, but such accumulations, as a rule, are not classified as natural gas deposits, and they have not yet found practical application. A significant amount of hydrocarbons is present in the Earth's mantle, but they are also of no interest.

Huge deposits of natural gas are concentrated in the sedimentary shell of the earth's crust. According to the theory of the biogenic (organic) origin of oil, they are formed as a result of the decomposition of the remains of living organisms. It is believed that natural gas is formed in the sedimentary shell at higher temperatures and pressures than oil. Consistent with this is the fact that gas fields are often deeper than oil fields.

Huge reserves of natural gas are possessed by Russia (Urengoyskoye field), the USA, Canada. Of other European countries, Norway is worth noting, but its reserves are small. Among the former republics of the Soviet Union, Turkmenistan has large gas reserves, as well as Kazakhstan (Karachaganak field).

In the second half of the 20th century at the University of I. M. Gubkin discovered natural gas hydrates (or methane hydrates). Later it turned out that the reserves of natural gas in this state are huge. They are located both underground and in a slight depression under the seabed.

Extraction and processing of natural gas

Gas fields

An oil or gas reservoir is an accumulation of hydrocarbons that fill the pores of permeable rocks. If the accumulation is large and its exploitation is economically feasible, the deposit is considered industrial. Deposits occupying large areas form deposits.

Gas drying

The moisture content of the gas during its transportation often causes serious operational difficulties. Under certain external conditions (temperature and pressure), moisture can condense, form ice plugs and crystalline hydrates, and in the presence of hydrogen sulfide and oxygen cause corrosion of pipelines and equipment. To avoid these difficulties, the gas is dried by lowering the dew point temperature by 5 ... 7 ° C below the operating temperature in the gas pipeline.

Gas purification from hydrogen sulfide and carbon dioxide

In combustible gases used for gas supply to cities, the content of hydrogen sulfide should not exceed 2 g per 100 m 3 of gas. The content of carbon dioxide is not limited by the norms, however, for technical and economic reasons, it should not exceed 2% in the transported gas.

Gas odorization

Natural gas is odorless. Therefore, in order to timely detect gas leaks, they give it a smell - the gas is odorized. Ethyl mercaptan (C 2 H 5 SH) is used as an odorant. In terms of toxicity, it is qualitatively and quantitatively identical to hydrogen sulfide, and has a sharp unpleasant odor.

Transportation

The main type of gas transport, at present, is pipeline. The gas moves through large-diameter pipes at a pressure of 75 atmospheres (7.5 MPa). Moving along the pipeline, the gas loses energy, it is spent on overcoming the friction force both between the pipe wall and the gas, and between the layers of the gas itself. In order for the pressure in the pipeline to be maintained at a given level, at a certain distance from each other, it is necessary to have compressor stations (CS), which must maintain the pressure in the pipeline at 75 atmospheres. The maintenance and construction of a pipeline costs a lot of money, but, nevertheless, the pipeline is the cheapest way to transport oil and gas.

Another way of transporting gas is the use of special tankers - gas carriers. These are specially equipped ships for the transportation of gas in a liquefied state under certain conditions. To transport gas by this method, it is necessary, in addition to the tankers themselves, to carry out a number of preparatory measures for the possibility of their use. It is necessary to stretch a gas pipeline to the seashore, build a port for tankers, a gas liquefaction plant, and the tankers themselves. Nevertheless, this type of gas transportation is economically justified if the consumer is more than 3,000 km away from production sites.

Synthesis of natural gas

There are many ways to obtain natural gas from other organic substances, such as waste from agricultural activities, woodworking and food industries, etc.