Fuel for cars. Liquefied, compressed gas. gas compression

In production processes associated with the use of gases (dispersion, mixing, pneumatic transport, drying, absorption, etc.), the movement and compression of the latter occurs due to the energy imparted to them by machines that bear the general name compression. At the same time, the productivity of compression plants can reach tens of thousands of cubic meters per hour, and the pressure varies within 10–8–10 3 atm., which leads to a wide variety of types and designs of machines used to move, compress and rarefy gases. Machines designed to create elevated pressures are called compressors, and machines that work to create a vacuum are called vacuum pumps.

Compression machines are classified mainly according to two criteria: the principle of operation and the degree of compression. Compression ratio is the ratio of the final gas pressure at the outlet of the machine R 2 to initial inlet pressure p 1 (i.e. p 2 /p 1).

According to the principle of operation, compression machines are divided into piston, bladed (centrifugal and axial), rotary and jet.

According to the degree of compression, they distinguish:

– compressors used to create high pressures, with a compression ratio R 2 /R 1 > 3;

- gas blowers used to move gases with high resistance of the gas pipeline network, while 3 > p 2 /p 1 >1,15;

- fans used to move large quantities of gas at p 2 /p 1 < 1,15;

- vacuum pumps that suck gas from a space with low pressure (below atmospheric) and pump it into a space with high (above atmospheric) or atmospheric pressure.

Any compression machines can be used as vacuum pumps; a deeper vacuum is created by reciprocating and rotary machines.

Unlike dropping liquids, the physical properties of gases are functionally dependent on temperature and pressure; the processes of movement and compression of gases are associated with internal thermodynamic processes. At low pressure and temperature differences, changes in the physical properties of gases during their movement at low velocities and pressures close to atmospheric are insignificant. This makes it possible to use all the basic provisions and laws of hydraulics to describe them. However, when deviating from normal conditions, especially at high degrees of gas compression, many positions of the hydraulics undergo a change.

1. Thermodynamic foundations of the gas compression process

The effect of temperature on the change in gas volume at constant pressure, as is known, is determined by the Gay-Lussac law, i.e., at p= const the volume of a gas is directly proportional to its temperature:

where V 1 and V 2 - gas volumes, respectively, at temperatures T 1 and T 2 expressed on the Kelvin scale.

The relationship between gas volumes at different temperatures can be represented by the relationship

, (4.1)

where V and V 0 - final and initial volumes of gas, m 3; t and t 0 – final and initial gas temperature, °С;β t– relative coefficient of volumetric expansion, deg. -one .

Change in gas pressure depending on temperature:

, (4.2)

where R and R 0 – final and initial gas pressure, Pa;β R– relative temperature coefficient of pressure, deg. -one .

Mass of gas M remains constant as the volume changes. If ρ 1 and ρ 2 are the densities of two temperature states of the gas, then
and
or
, i.e. The density of a gas at constant pressure is inversely proportional to its absolute temperature.

According to the Boyle-Mariotte law, at the same temperature, the product of the specific volume of gas v on the value of its pressure R is a constant value pv= const. Therefore, at constant temperature
, a
, i.e., the density of the gas is directly proportional to the pressure, since
.

Given the Gay-Lussac equation, one can obtain a relation relating the three parameters of a gas: pressure, specific volume, and its absolute temperature:

. (4.3)

The last equation is called Claiperon's equations. In general:

or
, (4.4)

where R is the gas constant, which is the work done by a unit mass of an ideal gas in isobaric ( p= const) process; when the temperature changes by 1°, the gas constant R has the dimension of J/(kgdeg):

, (4.5)

where l R is the specific work of volume change performed by 1 kg of ideal gas at constant pressure, J/kg.

Thus, equation (4.4) characterizes the state of an ideal gas. At a gas pressure over 10 atm, the use of this expression introduces an error in the calculations ( pv≠RT), therefore it is recommended to use formulas that more accurately describe the relationship between pressure, volume and temperature of a real gas. For example, the van der Waals equation:

, (4.6)

where R= 8314/M– gas constant, J/(kg K); M is the molecular weight of the gas, kg/kmol; a and in - quantities that are constant for a given gas.

Quantities a and in can be calculated from the critical gas parameters ( T kr and R cr):

;
. (4.7)

At high pressures, the value a/v 2 (additional pressure in the van der Waals equation) is small compared to the pressure p and it can be neglected, then equation (4.6) turns into the equation of state of a real Dupré gas:

, (4.8)

where the value in depends only on the type of gas and is independent of temperature and pressure.

In practice, to determine the parameters of a gas in its various states, thermodynamic diagrams are more often used: T–S(temperature–entropy), p–i(dependence of pressure on enthalpy), p–V(dependence of pressure on volume).

Figure 4.1 - T–S diagram

All gas parameters on the diagram T–S referred to 1 kg of gas.

Since according to the thermodynamic definition
, then the heat of change in the state of the gas
. Therefore, the area under the curve describing the change in the state of the gas is numerically equal to the energy (heat) of the change in state.

The process of changing the parameters of a gas is called the process of changing its state. Each state of the gas is characterized by the parameters p,v and T. In the process of changing the state of the gas, all parameters can change or one of them remains constant. Thus, a process occurring at constant volume is called isochoric, at constant pressure - isobaric, and at constant temperature isothermal. When, in the absence of heat exchange between the gas and the environment (heat is neither removed nor supplied), all three parameters of the gas change ( p,v,T) in expansion or contraction process , the process is called adiabatic, and when the change in gas parameters occurs with a continuous supply or removal of heat – polytropic.

With changing pressure and volume, depending on the nature of heat exchange with the environment, the change in the state of the gas in compression machines can occur isothermally, adiabatically and polytropically.

At isothermal process, the change in the state of the gas follows the Boyle–Mariotte law:

pv= const.

On the diagram p–v this process is depicted by a hyperbola (Fig. 4.2). Work 1 kg of gas l graphically represented by the shaded area, which is equal to
, i.e.

or
. (4.9)

The amount of heat that is released during isothermal compression of 1 kg of gas and that must be removed by cooling so that the temperature of the gas remains constant:

, (4.10)

where c v and c R are the specific heat capacities of the gas at constant volume and pressure, respectively.

On the diagram T–S process of isothermal compression of gas from pressure R 1 to pressure R 2 is shown as a straight line ab drawn between isobars R 1 and R 2 (Fig. 4.3).

The heat equivalent to the work of compression is represented by the area bounded by the extreme ordinates and the straight line ab, i.e.

. (4.11)

Figure 4.4 - Gas compression processes in the diagram
:

A is an adiabatic process;

B - isothermal process

At adiabatic In the process of gas compression, a change in its state occurs due to a change in its internal energy, and, consequently, in temperature.

In general form, the equation of an adiabatic process is described by the expression:

, (4.12)

where
is the adiabatic index.

Graphically (Fig. 4.4) this process on the diagram p–v is depicted as a steeper hyperbola than in Fig. 4.2., since k> 1.

If accept

, then
. (4.13)

Because the
and R= const, the resulting equation can be expressed differently:

or
. (4.14)

By appropriate transformations, one can obtain dependencies for other gas parameters:

;
. (4.15)

Thus, the gas temperature at the end of its adiabatic compression

. (4.16)

The work done by 1 kg of gas in an adiabatic process:

. (4.17)

The heat released during adiabatic compression of a gas is equivalent to the work expended:

Taking into account relations (4.15), the work on gas compression in the adiabatic process

. (4.19)

The process of adiabatic compression is characterized by the complete absence of heat exchange between the gas and the environment, i.e. dQ = 0, and dS = dQ/T, that's why dS = 0.

Thus, the process of adiabatic gas compression proceeds at a constant entropy ( S= const). On the diagram T–S this process is represented by a straight line AB(Fig. 4.5).

Figure 4.5 - Image of gas compression processes on the diagram T–S

If during compression the released heat is taken away in a smaller amount than is necessary for an isothermal process (which occurs in all real compression processes), then the actual work expended will be greater than during isothermal compression, and less than during adiabatic:

, (4.20)

where m is the polytropic index, k>m>1 (for air m
).

The value of the polytropic index m depends on the nature of the gas and the conditions of heat exchange with the environment. In compression machines without cooling, the polytropic exponent can be greater than the adiabatic exponent ( m>k), i.e., the process in this case proceeds along the superadiabatic.

The work expended on the rarefaction of gases is calculated using the same equations as the work on compressing gases. The only difference is that R 1 will be less than atmospheric pressure.

Polytropic compression process pressure gas R 1 up to pressure R 2 in fig. 4.5 will be depicted straight AC. The amount of heat released during polytropic compression of 1 kg of gas is numerically equal to the specific work of compression:

Gas compression end temperature

. (4.22)

Power, spent by compression machines for compression and rarefaction of gases, depends on their performance, design features, heat exchange with the environment.

Theoretical power expended on gas compression
, is determined by the productivity and specific work of compression:

, (4.23)

where G and V- mass and volumetric productivity of the machine, respectively;
is the density of the gas.

Therefore, for various compression processes, the theoretical power input is:

; (4.24)

; (4.25)

, (4.26)

where - volumetric performance of the compression machine, reduced to suction conditions.

The actual power expended is greater for a number of reasons; the energy consumed by the machine is higher than that which it transfers to the gas.

To evaluate the effectiveness of compression machines, a comparison of this machine with the most economical machine of the same class is used.

Refrigerated machines are compared to machines that would compress the gas isothermally under given conditions. In this case, the efficiency is called isothermal,  from:

, (4.27)

where N- the actual power expended by this machine.

If the machines operate without cooling, then the gas compression in them occurs along a polytrope, the exponent of which is higher than the adiabatic exponent ( m k). Therefore, the power expended in such machines is compared with the power that the machine would expend in the adiabatic compression of the gas. The ratio of these powers is the adiabatic efficiency:

. (4.28)

Taking into account the power lost to mechanical friction in the machine and taken into account by the mechanical efficiency. –  fur, power on the shaft of the compression machine:

or
. (4.29)

Engine power is calculated taking into account efficiency. the engine itself and efficiency. transfers:

. (4.30)

The installed power of the engine is taken with a margin (
):

. (4.31)

The value of  hell ranges from 0.930.97;  out depending on the degree of compression has a value of 0.640.78; mechanical efficiency varies within 0.850.95.

Gas that is extracted from the bowels of the earth or is a product of the processing of other hydrocarbons can subsequently be used in a liquefied or compressed form. What are the features of both options for the use of the respective fuel?

What is liquefied gas?

Under liquefied It is customary to understand natural gas, which is transferred from the initial, actually gaseous state into a liquid state - by cooling to a very low temperature, about minus 163 degrees Celsius. The volume of fuel is reduced by about 600 times.

Transportation of liquefied gas requires the use of special cryogenic tanks that are able to maintain the required temperature of the respective substance. The advantage of this type of fuel is the ability to deliver it to those places where it is problematic to lay conventional gas pipelines.

The conversion of liquefied gas to its original state also requires special infrastructure - regasification terminals. The processing cycle of the considered type of fuel - extraction, liquefaction, transportation and regasification - significantly increases the final cost of gas for the consumer.

The fuel in question is used, usually for the same purposes as natural gas in its original state - for heating rooms, ensuring the functioning of industrial equipment, power plants, as raw materials in some segments of the chemical industry.

What is compressed natural gas?

Under compressed, or compressed, it is customary to understand natural gas, which, like liquefied gas, is also presented in a liquid state, achieved, however, not by reducing the temperature of the fuel, but by increasing the pressure in the container in which it is placed. The volume of compressed gas is about 200 times less than that of the fuel in its original state.

Converting natural gas to liquid using high pressure is generally cheaper than liquefying fuel by lowering its temperature. The transportation of the considered type of gas is carried out in containers, as a rule, less technologically complex than cryocisters. Regasification of the corresponding type of fuel is not required: since it is under high pressure, it is easy to remove it from the tanks - it is enough to open the valves on them. Therefore, the cost of compressed gas for the consumer is in most cases lower than that which characterizes liquefied fuel.

Compressed gas is most often used as a fuel in various vehicles - cars, locomotives, ships, gas turbine engines of aircraft.

Comparison

The main difference between liquefied gas and compressed gas is that the first type of fuel is obtained by lowering the temperature of the initial gaseous substance, which is accompanied by its transformation into a liquid. Compressed gas is also a liquid fuel, but it is obtained by placing it in a container under high pressure. In the first case, the initial volume of gas exceeds the processed one (transferred to liquid) by about 600 times, in the second case, by 200 times.

It should be noted that liquefied gas is most often obtained by processing "classical" natural gas, which is represented mainly by methane. Compressed fuels are also made from many other naturally occurring gases such as propane or butane.

Having determined the difference between liquefied and compressed gas, we will reflect the conclusions in the table.

Table

The chemical composition of the gas. Application

The main part of natural gas is methane (CH4) - 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),

as well as other non-hydrocarbon substances:

hydrogen (H 2),

hydrogen sulfide (H 2 S),

carbon dioxide (CO 2),

helium (He).

Pure natural gas is colorless and odorless. In order to be able to identify a leak by smell, a small amount of substances with a strong unpleasant odor (so-called odorants) is added to the gas. The most commonly used odorant is ethyl mercaptan.

Hydrocarbon fractions are a valuable raw material for the chemical and petrochemical industries. They are widely used to produce acetylene. Pyrolysis of ethane produces ethylene, an important product for organic synthesis. During the oxidation of the propane-butane fraction, acetaldehyde, formaldehyde, acetic acid, acetone, and other products are formed. Isobutane is used for the production of high-octane components of motor fuels, as well as isobutylene, a raw material for the manufacture of synthetic rubber. Dehydrogenation of isopentane produces isoprene, an important product in the production of synthetic rubbers.

Compressed natural gas- Compressed natural gas used as motor fuel instead of gasoline, diesel fuel and propane.

Natural gas, like any other, can be compressed with a compressor. At the same time, the volume occupied by them is significantly reduced. Natural gas is traditionally compressed to a pressure of 200–250 bar, resulting in a volume reduction of 200–250 times. Gas is compressed (compressed) for transportation through main gas pipelines, to maintain the correct pressure inside the reservoir (reservoir pressure) during injection underground, and the production of compressed natural gas is an intermediate step in the production of liquefied natural gas. Compressed natural gas is cheaper than conventional fuels, and the greenhouse effect caused by its combustion products is less compared to conventional fuels, so it is safer for environment. Storage and transportation of compressed natural gas takes place in special gas storage tanks. The addition of biogas to compressed natural gas is also used, which reduces carbon emissions into the atmosphere.

Compressed natural gas as a fuel has a number of advantages:

· Methane (the main component of natural gas) is lighter than air and in the event of an accidental spill it evaporates quickly, unlike the heavier propane that accumulates in natural and artificial depressions and creates an explosion hazard.

· Not toxic in small concentrations;

· Does not cause corrosion of metals.

· Compressed natural gas is cheaper than any oil fuel, including diesel, but surpasses them in terms of calorific value.

· Low boiling point guarantees complete evaporation of natural gas at the lowest ambient temperatures.

· Natural gas burns almost completely and does not leave soot, deteriorating the environment and reducing efficiency. The removed flue gases do not contain sulfur impurities and do not destroy the metal of the chimney.

· Operating costs for gas boilers are also lower than traditional ones.

Another feature of compressed natural gas is that boilers running on natural gas have a higher efficiency - up to 94%, do not require fuel consumption for preheating it in winter (like oil and propane-butane).

Natural gas, cooled after purification from impurities to a condensation temperature (-161.5 0 C), turns into a liquid called liquefied natural gas. Liquefied gas is a colorless, odorless liquid, the density of which is half that of water. 75-99% consists of methane. Boiling point -158 ... -163 0 C. In the liquid state, it is non-flammable, non-toxic, non-aggressive. For use, it is subjected to evaporation to its original state. When the vapors are burned, carbon dioxide and water vapor are produced. The volume of gas during liquefaction is reduced by 600 times, which is one of the main advantages of this technology. The liquefaction process takes place in stages, at each of which the gas is compressed 5-12 times, then cooled and transferred to the next stage. The actual liquefaction occurs during cooling after the last stage of compression. The liquefaction process thus requires a significant amount of energy - up to 25% of its amount contained in liquefied gas. Liquefied gas is produced in the so-called liquefaction plants (plants), after which it can be transported in special cryogenic containers - sea tankers or tanks for land transport. This makes it possible to deliver gas to areas that are far from the main gas pipelines traditionally used to transport conventional natural gas. Natural gas in liquefied form is stored for a long time, which allows you to create reserves. Before delivery directly to the consumer, liquefied natural gas is returned to its original gaseous state at regasification terminals. The first attempts to liquefy natural gas for industrial purposes date back to the beginning of the 20th century. In 1917, the first liquefied natural gas was produced in the USA, but the development of pipeline delivery systems delayed the improvement of this technology for a long time. In 1941, another attempt was made to produce LNG, but production reached industrial scale only from the mid-1960s. In Russia, the construction of the first liquefied natural gas plant began in 2006 as part of the Sakhalin-2 project. The grand opening of the plant took place in the winter of 2009.

Shale gas- natural gas extracted from shale, consisting mainly of methane. The first commercial shale gas well was drilled in the United States in 1821. Large-scale commercial production of shale gas was started by Devon Energy in the United States in the early 2000s at the Barnett Shale field, which drilled the first horizontal well in this field in 2002. Thanks to a sharp increase in its production, called the "gas revolution", in 2009 the United States became the world leader in gas production (745.3 billion m 3), with more than 40% coming from unconventional sources (coal bed methane and shale gas).

Shale gas resources in the world amount to 200 trillion m 3 . In January 2011, economist A.D. Haitun wrote about the possibility that shale gas "will follow the fate of coal-fired methane with a significant drop in production growth during long-term operation of fields, or the fate of biofuels, the vast majority of world production of which is in America, and is now declining."

Gas reserves and resources

The world geological reserves of combustible gases on the continents, in the zone of shelves and shallow seas, according to forecast estimates, reach 10 15 m 3 , which is equivalent to 10 12 tons of oil.

The largest deposits in the USSR were: Urengoy (4 trillion m 3) and Zapolyarnoye (1.5 trillion m 3), Vuktylskoye (452 ​​billion m 3), Orenburg (650 billion m 3), Stavropolskoye (220 billion m 3), Gazli (445 billion m 3) in Central Asia; Shebslinskoye (390 bcm) in Ukraine.

On the Yamal Peninsula and in adjacent water areas, 11 gas and 15 oil and gas condensate fields have been discovered, the explored and preliminary estimated (АВС 1 + С 2) gas reserves are about 16 trillion m 3, promising and predicted (С 3 -D 3) gas resources are about 22 trillion m 3. The most significant Yamal field in terms of gas reserves is Bovanenkovskoye - 4.9 trillion m 3 (АВС 1 + С 2), which will begin to be developed in 2012, and the gas will be supplied to the new main gas pipeline Bovanenkovo-Ukhta. The initial reserves of the Kharasaveyskoye, Kruzenshternskoye and Yuzhno-Tambeyskoye fields are about 3.3 trillion m 3 of gas.

Eastern Siberia and the Far East make up about 60% of the territory of the Russian Federation. The initial total gas resources onshore in the East of Russia are 52.4 trillion m 3 , on the shelf - 14.9 trillion m 3 .

In Russia, gas production by Gazprom alone in 2011 amounted to 513.2 bcm. At the same time, the increase in category C 1 reserves reached a record level - 686.4 billion m 3, condensate - 38.6 million tons. In 2012, it is planned to produce 528.6 billion m 3 of gas and 12.8 million tons of gas condensate.

Condensate

Condensate– liquid product of separation of natural gases. It is represented mainly by liquid hydrocarbons under normal conditions - pentane and heavier hydrocarbons of alkane, cyclane and arene composition. The density usually does not exceed 0.785 g/cm 3 , although differences with densities up to 0.82 g/cm 3 are known. The end of the boil is from 200 to 350 0 C.

Distinguish raw condensate from separation, and stable obtained by deep degassing of raw condensate. The amount of condensate in reservoir gases is expressed either by the ratio of its volume to the volume of separated gas (cm 3 /m 3) and is called condensate factor. The amount of condensate related to 1 m 3 of separated (free) gas reaches 700 cm 3 . Depending on the value of the condensate factor, gases are "dry" (less than 10 cm 3 /m 3), "lean" (10-30 cm 3 /m 3) and "fat" (30-90 cm 3 /m 3). Gases characterized by a GOR greater than 90 cm 3 /m 3 are called gas condensate. At the Vuktyl oil and gas condensate field, the condensate factor is 488-538 cm 3 /m 3, natural gases from Western Siberia fields are usually “dry”.

Instruction

Looks like liquefied natural gas(LNG) is a colorless liquid, odorless, 75-90% composed and has very important properties: in the liquid state, it is not combustible, not aggressive, which is extremely important during transportation. The LNG liquefaction process has a character, where each new stage means compression by 5-12 times, followed by cooling and moving to the next stage. LNG becomes liquid upon completion of the last stage of compression.

If gas needs to be transported over very long distances, then it is much more profitable to use special vessels - gas carriers. From the place of gas to the nearest suitable place on the sea coast, a pipeline is being pulled, and a terminal is being built on the coast. There, the gas is highly compressed and cooled, turning it into a liquid state, and pumped into isothermal tanks of tankers (at temperatures of the order of -150 ° C).

This method of transportation has a number of advantages over pipeline transportation. Firstly, one of these in one flight can carry a huge amount of gas, because the density of a substance in a liquid state is much higher. Secondly, the main costs are not for transportation, but for loading and unloading the product. Thirdly, storage and transportation of liquefied gas is much safer than compressed gas. There can be no doubt that the share of natural gas transported in liquefied form will steadily increase compared to pipeline supplies.

Liquefied natural gas in demand in various fields of human activity - in industry, in road transport, in medicine, in agriculture, in science, etc. Liquefied gas We won due to the convenience of their use and transportation, as well as environmental friendliness and low cost.

Instruction

Before liquefying hydrocarbon gas and it must first be cleaned and removed water vapor. Carbonic gas removed using a three-stage molecular filter system. Purified in this way gas in small quantities it is used as a regeneration. Recoverable gas either incinerated or used to generate power in generators.

Drying occurs with the help of 3 molecular filters. One filter absorbs water vapor. Another dries gas, which goes further and passes through the third filter. To lower the temperature gas passed through a water cooler.

The nitrogen method involves the production of liquefied hydrocarbon gas and from any gas new sources. The advantages of this method include the simplicity of technology, the level of safety, flexibility, ease and low cost of operation. The limitations of this method are the need for a power source and high capital costs.

With a mixed method for the production of liquefied gas and a mixture of nitrogen and is used as a refrigerant. receive gas also from any source. This method features a flexible production cycle and low variable production costs. Compared to the nitrogen liquefaction process, capital costs are more significant here. A source of electricity is also needed.

Sources:

• What is gas liquefaction?
• Liquefied gas: receipt, storage and transportation
• what is liquefied gas

Natural gas is extracted from the bowels of the Earth. This mineral consists of a mixture of gaseous hydrocarbons, which is formed as a result of the decomposition of organic matter in sedimentary rocks of the earth's crust.

What are the ingredients in natural gas

80-98% natural gas consists of (CH4). It is the physicochemical properties of methane that determine the characteristics of natural gas. Along with methane, natural gas contains compounds of the same structural type - ethane (C2H6), propane (C3H8) and butane (C4H10). In some cases, in small quantities, from 0.5 to 1%, natural gas contains: (С5Н12), (С6Н14), heptane (С7Н16), (С8Н18) and nonane (С9Н20).

Natural gas also includes compounds of hydrogen sulfide (H2S), carbon dioxide (CO2), nitrogen (N2), helium (He), water vapor. The composition of natural gas depends on the characteristics of the fields where it is produced. Natural gas produced in pure gas fields consists mainly of methane.

Characteristics of natural gas constituents

All chemical compounds that make up natural gas have a number of properties that are useful in various industries and in everyday life.

Methane is a colorless, odorless, flammable gas that is lighter than air. It is used in industry and everyday life as a fuel. Ethane is a colorless, odorless, combustible gas that is slightly heavier than air. Basically, ethylene is obtained from. Propane is a poisonous, colorless and odorless gas. Butane is close to him in properties. Propane is used, for example, in welding work, in the processing of scrap metal. Liquefied and butane fill lighters and gas cylinders. Butane is used in refrigeration.

Pentane, hexane, heptane, octane and nonane -. Pentane is present in small amounts in motor fuels. Hexane is also used in the extraction of vegetable oils. Heptane, hexane, octane and nonane are good organic solvents.

Hydrogen sulfide is a poisonous colorless heavy gas, rotten eggs. This gas, even in small concentrations, causes paralysis of the olfactory nerve. But due to the fact that hydrogen sulfide has good antiseptic properties, it is used in small doses in medicine for hydrogen sulfide baths.

Carbon dioxide is a non-flammable, colorless, odorless gas with a sour taste. Carbon dioxide is used in the food industry: in the production of carbonated drinks to saturate them with carbon dioxide, to freeze food, to cool cargo during transportation, etc.

Nitrogen is a harmless colorless gas, odorless and tasteless. It is used in the production of mineral fertilizers, used in medicine, etc.

Helium is one of the lightest gases. It is colorless and odorless, non-flammable, non-toxic. Helium is used in various industries - for cooling nuclear reactors, filling stratospheric balloons.

One of the many reasons for the slowness in the gasification of transport is that the range of gas motor fuels is quite extensive:

• liquefied petroleum gas (LPG);
• compressed (compressed) natural gas (CNG);
• liquefied natural gas (LNG).

The main advantages of gas motor fuel are its price, price and again price. So far, these advantages outweigh the numerous and versatile disadvantages.

Liquefied petroleum gas (LPG)

This gas is a mixture of C3H8 propane and C4H10 butane, extracted from associated petroleum gases, from natural gas condensate fractions, from gases of oil and condensate stabilization processes, from refinery gases obtained from oil refining plants. In addition to propane and butane, oil gas contains, by mass, about 6% of other hydrocarbons - ethane, ethylene, propylene, butylene and their isomers, that is, the composition of the LPG is heterogeneous and unstable. To control leaks, malodorous substances - mercaptans - are introduced into the composition of the LPG. Mercaptans are easy to identify with your nose when a gas-cylinder GAZelle passes you on the street.

The main advantage of propane and butane is in high critical temperature. The critical temperature is the temperature at which the density of the liquid and its saturated vapor become equal and the interface between them disappears.

Propane has a critical temperature of 96.8 °C, butane has a critical temperature of 152.0 °C, which makes it easy to liquefy these gases and store them in a liquid state at a relatively low pressure of up to 1.6 MPa. This also means that the LPG storage vessel will be relatively light, and the gas can be stored in a liquefied state for an arbitrarily long time, provided that the vessel is completely sealed. However, the LPG cylinder is a pressure vessel and cannot be molded into any shape, like a gas tank, for example. This circumstance gives rise to problems with the placement of the gas cylinder on the machine.

For refueling vehicles, two CIS brands are used: summer and winter. Summer brand, or automobile propane-butane (PBA), contains 50 ± 10% propane by weight. Winter, or automobile propane (PA), contains 85 ± 10% propane by weight. Thus, by adjusting the content of light propane, year-round operation of LPG vehicles is ensured.

The use of LPG is limited to gasoline engines, i.e. engines with a low compression ratio and spark ignition. These are passenger cars, light and medium-duty trucks and power plants. LPG consumption is 10–15% higher than gasoline due to lower volumetric calorific value: 1 liter of gasoline will be equivalent to 1.1–1.15 m 3 of LPG, and in real conditions due to a drop in engine power - 1.15– 1.3 m 3 CIS. At low temperatures, the engine is started on gasoline; after warming up, the driver can switch to gas directly from the cab. You can switch from one type of fuel to another on the go.

Propane-butane is 1.5–2 times heavier than air and, when leaked, accumulates near the ground, creating an explosive and unhealthy atmosphere. Therefore, gas-balloon cars are stored in open parking lots, and repair areas are equipped with good ventilation. Prolonged inhalation of propane-butane is not only unpleasant due to mercaptans, but also leads to poor health, up to poisoning.

LPG has an octane rating of around 105 and no detonation is claimed to occur in any mode of engine operation. This statement should not serve as a reason for complacency; with a certain inquisitiveness of the mind, detonation can be achieved.

Taking into account the cost of equipping with gas equipment, its weight and a smaller power reserve at one gas station, switching a car to LPG remains profitable due to the price. Passenger cars and light trucks have been and remain the driving force behind the advancement of the CIS to the masses. Liquefied petroleum gases are produced by the same companies as a by-product of the production of liquid fuels, which affects the number of gas stations - companies are interested in marketing their own product.

As for diesel engines, propane-butane has no prospects here due to the instability of combustion at a high compression ratio. This is the main reason why LPG has not taken root on diesels. But the potential of the CIS has not yet been fully revealed.

General information about methane

Natural gases are understood as methane CH4 - the simplest hydrocarbon without color and odor. Methane is the third most abundant gas in the universe after hydrogen and helium. There is no final opinion about the origin of natural gas deposits in the earth's crust, as well as about the origin of oil.

Natural gas contains from 70 to 98% methane, the rest is heavier hydrocarbons: ethane, propane and butane, as well as non-hydrocarbons: water, hydrogen sulfide, carbon dioxide, nitrogen, helium and other inert gases. Before being supplied to the gas transmission system (GTS), natural gas must be cleaned and dried, getting rid of water, hydrogen sulfide, heavy hydrocarbons and other impurities should be separated. In the pipeline, water vapor can condense or form crystalline compounds with gas - hydrates - and accumulate on the bends of the pipeline, making it difficult for the gas to move. Hydrogen sulfide causes severe corrosion of gas equipment. Depending on the composition of natural gas, various technologies for drying and separating gases are used. Thus, pure methane with minor impurities remains. Through the GTS, methane is supplied to consumers. If your home is connected to a gas distribution system, then it is methane that burns in your kitchen in the burner. The same methane, after compression or liquefaction, is used to fill gas-balloon equipment.

Methane is an odorless gas, with a characteristic aroma ("If you smell gas, call 09") it is given by mercaptans, which are injected into the gas before injection into the GTS (16 g per 1000 m 3). This method was invented to detect leaks from the GTS, which stretches for thousands of kilometers. When leaked, the mercaptan fragrance attracts crows, which are easy to spot when helicopters fly around the pipeline.

Methane is 1.6 times lighter than air and immediately volatilizes when it leaks. Methane is explosive at concentrations in air from 4.4 to 17%. The most explosive concentration is 9.5%. It is easy to determine the presence of methane in the air by mercaptan aromas. In places of natural formation of methane, where it is impossible to determine it by smell, for example, in mines, gas analyzers are used. The first mine gas analyzers were canaries. LPG equipment is stored in open parking lots, and closed repair areas are equipped with forced exhaust ventilation. On the main gas, without any preparation, power plants of various capacities connected directly to the pipe operate.

Compressed natural gases (CNG)

The critical temperature of methane is –82.3 °C, and its liquefaction is very expensive, therefore methane as a gas motor fuel is used mainly in a compressed (compressed) form, while the gas is reduced in volume by 200–250 times. A gas pipeline is brought to the automobile gas-filling compressor station (CNG) and the gas is compressed on site. They compress, or rather, pressurize the main gas with a compressor up to 20 MPa and dry it. At the station, the CNG is stored in a small pressure vessel from which the gas is pumped into the vehicle's cylinders. As for the transportation of finished CNG, special gas carriers are used for this, which are a battery of cylinders, small in volume compared to a tank for liquefied gases, that is, the transportation of finished CNG is an expensive and specific task. The supply of main gas to the filling station is necessary, which somewhat complicates the expansion of the network of gas filling stations. Today, in 58 regions of the Russian Federation, there are 246 CNG filling compressor stations (CNG filling stations) that fill CNG vehicles. The undisputed leader of the national NGV market is Gazprom, which owns 210 CNG filling stations. For more than 10 years, Gazprom has been promoting natural gas motor fuel in Russia - CNG filling stations are available in 70% of the regions, and not in all, 246 CNG filling stations are 1% of all filling stations in the Russian Federation, and the undisputed leader put into operation 2.1 CNG filling stations in year.

The high pressure of CNG requires very strong, thick-walled, heavy cylinders. But that's not all. CNG can drive 3.5 times less distance than LPG with equal volumes of gas cylinders. Either to be weighed down with cylinders, or to be frequently refueled - this is the main disadvantage of CNG, which determines the scope of its application: near the gas station, as well as the types of engines running on them.

Due to the fact that a significant space is needed to accommodate CNG cylinders, this type of fuel is of interest for medium and large-capacity vehicles and tractor equipment. Dual-fuel engines are of the greatest interest today - gas-diesels running on diesel fuel and CNG, precisely because of the meager infrastructure of CNG, so that there is something to get to the gas station. Under the second type of fuel, the diesel engine is converted relatively simply and quickly, the injection of diesel fuel into the combustion chamber serves to ignite the combustible mixture. Manufacturers of gas equipment have achieved a ratio of diesel fuel and methane consumption of 20:80 on mainline tractors with a Common Rail fuel system and 30:70 on tractor equipment with high-pressure fuel pumps. Converting a car to CNG is 3-4 times more expensive than a similar operation with LPG, however, the costs are paid back in about a year due to the difference in the price of gas and diesel fuel.

Mechanical engineering also offers single-fuel CNG engines with a reduced compression ratio and spark ignition. You have to understand that such cars are literally chained to the gas station.

CNG is an excellent fuel for diesel engines. Methane 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. Methane burns completely without forming solid particles and ash, which cause increased wear of the cylinder-piston group. 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. Methane is environmentally friendly: it gives a very clean exhaust. And most importantly, CNG costs three times cheaper than gasoline and diesel fuel, although in fact it should cost even less.

Liquefied natural gas (LNG)

When liquefied, methane is reduced in volume by 600 times - this is the main advantage of liquefaction, which determines the scope of its application: buses, main tractors, mining dump trucks, that is, where fuel tanks should take up space to a minimum, and accommodate to the maximum. The same volume holds three times more LNG than CNG.

Liquefaction takes place at a temperature of -161.5 °C. The process is energy-intensive and requires cryogenic equipment. Liquefied methane is stored at a temperature inside a thermally insulated vessel from -160 to -196 °C. Very high quality thermal insulation is required. And just like with CNG, diesel engines are being converted to dual-fuel ones. Automotive LNG equipment is distinguished by a thermos bottle and an evaporator, the rest of the components are the same.

Liquefied methane is even less common than compressed. Some bus depots built gas filling stations. These experiments are still more experimental in nature.

Conclusion

When there are discussions about gas motor fuel and its slow distribution, the question is always raised as to what comes first: a fleet of gas-filled vehicles or a network of gas filling stations. It is absolutely clear that the filling network is primary. Hence the age-old question: who is to blame? Gas station owners. Owners are not interested in what the country is interested in, because they do not see profit in that. The owners will continue to sabotage the gasification of transport.

What to do? The only effective means of combating natural monopolies and stimulating the economy as a whole remains the nationalization, first of all, of PJSC Gazprom, all its subsidiaries and all gas distribution networks. It is unsuitable for enterprises that solve economic and social problems on the scale of the Russian Federation, constituent entities and parts of constituent entities of the Federation, to serve to satisfy the ambitions of a narrow circle of individuals. Regulation of tariffs in this direction is nothing more than a palliative.