What is the calorific value of natural gas. Calorific value of gases

Every day, turning on the burner on the kitchen stove, few people think about how long ago gas production began. In our country, its development began in the twentieth century. Before this, it was simply found during the extraction of petroleum products. The calorific value of natural gas is so great that today this raw material is simply irreplaceable, and its high-quality analogues have not yet been developed.

The calorific value table will help you choose fuel for heating your home

Features of fossil fuels

Natural gas is an important fossil fuel that occupies a leading position in the fuel and energy balances of many countries. In order to supply fuel to the city and all kinds of technical enterprises consume various flammable gases, since natural gas is considered dangerous.

Environmentalists believe that gas is the cleanest fuel; when burned, it emits much less toxic substances than firewood, coal, oil. This fuel is used daily by people and contains an additive such as an odorant; it is added in equipped installations in a ratio of 16 milligrams per 1 thousand cubic meters of gas.

An important component of the substance is methane (approximately 88-96%), the rest is other chemicals:

butane;
hydrogen sulfide;
propane;
nitrogen;
oxygen.

In this video we will look at the role of coal:

The amount of methane in natural fuel directly depends on its deposit.

The described type of fuel consists of hydrocarbon and non-hydrocarbon components. Natural fossil fuels are primarily methane, which includes butane and propane. Apart from the hydrocarbon components, the described fossil fuel contains nitrogen, sulfur, helium and argon. Liquid vapors are also found, but only in gas and oil fields.

Types of deposits

There are several types of gas deposits. They are divided into the following types:

gas;
oil.

Their distinctive feature is the hydrocarbon content. Gas deposits contain approximately 85-90% of the present substance, oil fields contain no more than 50%. The remaining percentages are occupied by substances such as butane, propane and oil.

A huge disadvantage of oil production is its flushing from various kinds additives Sulfur is used as an impurity in technical enterprises.

Natural gas consumption

Butane is consumed as fuel at gas stations for cars, and organic matter, called “propane”, is used to refill lighters. Acetylene is a highly flammable substance and is used in welding and metal cutting.

Fossil fuels are used in everyday life:

columns;
gas stove;

This type of fuel is considered the most inexpensive and harmless; the only drawback is the release of carbon dioxide into the atmosphere when burned. Scientists all over the planet are looking for a replacement for thermal energy.

Calorific value

The calorific value of natural gas is the amount of heat generated when a unit of fuel is sufficiently burned. The amount of heat released during combustion is referred to as one cubic meter taken in natural conditions.

The thermal capacity of natural gas is measured in the following indicators:

kcal/nm 3 ;
kcal/m3.

There is high and low calorific value:

High. Considers the heat of water vapor generated during fuel combustion.
Low. It does not take into account the heat contained in water vapor, since such vapors cannot be condensed, but leave with combustion products. Due to the accumulation of water vapor, it forms an amount of heat equal to 540 kcal/kg. In addition, when the condensate cools, heat comes out from 80 to one hundred kcal/kg. In general, due to the accumulation of water vapor, more than 600 kcal/kg is formed, this is the distinguishing feature between high and low heat output.

For the vast majority of gases consumed in the urban fuel distribution system, the difference is equal to 10%. In order to provide cities with gas, its calorific value must be more than 3500 kcal/nm 3 . This is explained by the fact that the supply is carried out through a pipeline over long distances. If the calorific value is low, then its supply increases.

If the calorific value of natural gas is less than 3500 kcal/nm 3, it is more often used in industry. It does not need to be transported over long distances, and combustion becomes much easier. Serious changes in the calorific value of gas require frequent adjustment and sometimes replacement large quantity standardized burners of household sensors, which leads to difficulties.

This situation leads to an increase in gas pipeline diameters, as well as increased costs for metal, network installation and operation. Big disadvantage low-calorie fossil fuels is huge content carbon monoxide, in connection with this, the level of threat during fuel operation and pipeline maintenance, in turn, as well as equipment, increases.

The heat released during combustion, not exceeding 3500 kcal/nm 3, is most often used in industrial production, where it is not necessary to transfer it over a long distance and easily cause combustion.

Gas fuel is divided into natural and artificial and is a mixture of flammable and non-flammable gases containing a certain amount of water vapor and sometimes dust and tar. The amount of gas fuel is expressed in cubic meters at normal conditions(760 mmHg and 0°C), and the composition is expressed as a percentage by volume. The composition of the fuel is understood as the composition of its dry gaseous part.

Natural gas fuel

The most common gas fuel is natural gas, which has a high calorific value. The basis of natural gas is methane, the content of which is 76.7-98%. Other gaseous hydrocarbon compounds comprise natural gas from 0.1 to 4.5%.

Liquefied gas petroleum product - consists mainly of a mixture of propane and butane.

Natural gas (CNG, NG): methane CH4 more than 90%, ethane C2 H5 less than 4%, propane C3 H8 less than 1%

Liquefied gas (LPG): propane C3 H8 more than 65%, butane C4 H10 less than 35%

The composition of flammable gases includes: hydrogen H2, methane CH4, Other hydrocarbon compounds CmHn, hydrogen sulfide H2S and non-flammable gases, carbon dioxide CO2, oxygen O2, nitrogen N2 and a small amount of water vapor H2O. Indexes m And n at C and H characterize compounds of various hydrocarbons, for example for methane CH 4 t = 1 and n= 4, for ethane C 2 N b t = 2 And n= b, etc.

Composition of dry gaseous fuel (percentage by volume):

CO + H 2 + 2 C m H n + H 2 S + CO 2 + O 2 + N 2 = 100%.

The non-combustible part of dry gas fuel - ballast - consists of nitrogen N and carbon dioxide CO 2.

The composition of wet gaseous fuel is expressed as follows:

CO + H 2 + Σ C m H n + H 2 S + CO 2 + O 2 + N 2 + H 2 O = 100%.

The heat of combustion, kJ/m (kcal/m3), 1 m3 of pure dry gas under normal conditions is determined as follows:

Q n s = 0.01,

where Qso, Q n 2, Q c m n n Q n 2 s. - heat of combustion of individual gases included in the mixture, kJ/m 3 (kcal/m 3); CO, H 2, Cm H n, H 2 S - components that make up gas mixture,% by volume.

The calorific value of 1 m3 of dry natural gas under normal conditions for most domestic fields is 33.29 - 35.87 MJ/m3 (7946 - 8560 kcal/m3). Characteristics of gaseous fuel are given in Table 1.

Example. Determine the lower calorific value of natural gas (under normal conditions) of the following composition:

H 2 S = 1%; CH 4 = 76.7%; C 2 H 6 = 4.5%; C 3 H 8 = 1.7%; C 4 H 10 = 0.8%; C 5 H 12 = 0.6%.

Substituting the characteristics of gases from Table 1 into formula (26), we obtain:

Q ns = 0.01 = 33981 kJ/m 3 or

Q ns = 0.01 (5585.1 + 8555 76.7 + 15 226 4.5 + 21 795 1.7 + 28 338 0.8 + 34 890 0.6) = 8109 kcal/m3.

Table 1. Characteristics of gaseous fuel

Gas	Designation	Heat of combustion Q n s
Gas	Designation	KJ/m3	Kcal/m3
Hydrogen	N,	10820	2579
Carbon monoxide	CO	12640	3018
Hydrogen sulfide	H 2 S	23450	5585
Methane	CH 4	35850	8555
Ethane	C 2 H 6	63 850	15226
Propane	C 3 H 8	91300	21795
Butane	C 4 H 10	118700	22338
Pentane	C 5 H 12	146200	34890
Ethylene	C 2 H 4	59200	14107
Propylene	C 3 H 6	85980	20541
Butylene	C 4 H 8	113 400	27111
Benzene	C 6 H 6	140400	33528

DE type boilers consume from 71 to 75 m3 of natural gas to produce one ton of steam. The cost of gas in Russia as of September 2008. is 2.44 rubles per cubic meter. Therefore, a ton of steam will cost 71 × 2.44 = 173 rubles 24 kopecks. The real cost of a ton of steam at factories is for boilers DE is at least 189 rubles per ton of steam.

DKVR type boilers consume from 103 to 118 m3 of natural gas to produce one ton of steam. The minimum estimated cost of a ton of steam for these boilers is 103 × 2.44 = 251 rubles 32 kopecks. The real cost of steam at factories is no less than 290 rubles per ton.

How to calculate the maximum natural gas consumption for a DE-25 steam boiler? This technical specifications boiler 1840 cubes per hour. But you can also calculate. 25 tons (25 thousand kg) must be multiplied by the difference between the enthalpies of steam and water (666.9-105) and all this divided by the boiler efficiency of 92.8% and the heat of combustion of the gas. 8300. and that's it

Artificial gas fuel

Artificial combustible gases are a fuel of local importance because they have a significantly lower calorific value. Their main combustible elements are carbon monoxide CO and hydrogen H2. These gases are used within the production where they are obtained as fuel for technological and power plants.

All natural and artificial flammable gases are explosive and can ignite in an open flame or spark. There are lower and upper explosive limits of gas, i.e. its highest and lowest percentage concentration in the air. The lower explosive limit of natural gases ranges from 3% to 6%, and the upper limit - from 12% to 16%. All flammable gases can cause poisoning to the human body. The main toxic substances of flammable gases are: carbon monoxide CO, hydrogen sulfide H2S, ammonia NH3.

Natural flammable gases and artificial ones are colorless (invisible) and odorless, which makes them dangerous if they penetrate into the interior of the boiler room through leaks in gas pipeline fittings. To avoid poisoning, flammable gases should be treated with an odorant - a substance with an unpleasant odor.

Production of carbon monoxide CO in industry by gasification of solid fuel

For industrial purposes, carbon monoxide is obtained by gasification of solid fuel, i.e., converting it into gaseous fuel. This way you can get carbon monoxide from any solid fuel - fossil coal, peat, firewood, etc.

The process of gasification of solid fuel is shown in a laboratory experiment (Fig. 1). Having filled the refractory tube with pieces of charcoal, we heat it strongly and let oxygen pass through from the gasometer. We pass the gases coming out of the tube through a washer with lime water and then set it on fire. The limewater becomes cloudy and the gas burns with a bluish flame. This indicates the presence of CO2 dioxide and carbon monoxide CO in the reaction products.

The formation of these substances can be explained by the fact that when oxygen comes into contact with hot coal, the latter is first oxidized into carbon dioxide: C + O 2 = CO 2

Then, passing through hot coal, carbon dioxide is partially reduced to carbon monoxide: CO 2 + C = 2CO

Rice. 1. Production of carbon monoxide (laboratory experiment).

IN industrial conditions Gasification of solid fuel is carried out in furnaces called gas generators.

The resulting mixture of gases is called generator gas.

The gas generator device is shown in the figure. It is a steel cylinder with a height of about 5 m and a diameter of approximately 3.5 m, lined inside with refractory bricks. The gas generator is loaded with fuel from above; From below, air or water vapor is supplied by a fan through the grate.

Oxygen in the air reacts with carbon in the fuel to form carbon dioxide, which, rising through the layer of hot fuel, is reduced by carbon to carbon monoxide.

If only air is blown into the generator, the result is a gas that contains carbon monoxide and air nitrogen (as well as a certain amount of CO 2 and other impurities). This generator gas is called air gas.

If water vapor is blown into a generator with hot coal, the reaction results in the formation of carbon monoxide and hydrogen: C + H 2 O = CO + H 2

This mixture of gases is called water gas. Water gas has a higher calorific value than air gas, since its composition, along with carbon monoxide, also includes a second flammable gas - hydrogen. Water gas (synthesis gas), one of the products of gasification of fuels. Water gas consists mainly of CO (40%) and H2 (50%). Water gas is a fuel (heat of combustion 10,500 kJ/m3, or 2730 kcal/mg) and at the same time a raw material for the synthesis of methyl alcohol. Water gas, however, cannot be obtained for a long time, since the reaction of its formation is endothermic (with heat absorption), and therefore the fuel in the generator cools down. To keep the coal hot, the injection of water vapor into the generator is alternated with the injection of air, the oxygen of which is known to react with the fuel to release heat.

IN lately Steam-oxygen blasting began to be widely used for fuel gasification. Simultaneous blowing of water vapor and oxygen through the fuel layer allows the process to be carried out continuously, significantly increasing the productivity of the generator and obtaining gas from high content hydrogen and carbon monoxide.

Modern gas generators are powerful devices of continuous operation.

To prevent flammable and toxic gases from penetrating into the atmosphere when fuel is supplied to the gas generator, the loading drum is made double. While fuel enters one compartment of the drum, fuel is poured into the generator from another compartment; when the drum rotates, these processes are repeated, but the generator remains isolated from the atmosphere all the time. Uniform distribution of fuel in the generator is carried out using a cone, which can be installed at different heights. When it is lowered, the coal falls closer to the center of the generator; when the cone is raised, the coal is thrown closer to the walls of the generator.

Removal of ash from the gas generator is mechanized. The cone-shaped grate is slowly rotated by an electric motor. In this case, the ash is displaced towards the walls of the generator and, using special devices, is dumped into the ash box, from where it is periodically removed.

The first gas lamps were lit in St. Petersburg on Aptekarsky Island in 1819. The gas used was obtained by gasification of coal. It was called illuminating gas.

The great Russian scientist D.I. Mendeleev (1834-1907) first expressed the idea that gasification of coal can be carried out directly underground, without lifting it out. The tsarist government did not appreciate this proposal from Mendeleev.

The idea of underground gasification was warmly supported by V.I. Lenin. He called it “one of the great victories of technology.” Underground gasification was carried out for the first time by the Soviet state. Already before the Great Patriotic War, underground generators were operating in the Donetsk and Moscow Region coal basins in the Soviet Union.

An idea of one of the methods of underground gasification is given in Figure 3. Two wells are laid into the coal seam, which are connected below by a channel. Coal is set on fire in such a channel near one of the wells and blast is supplied there. Combustion products, moving along the channel, interact with hot coal, resulting in the formation of combustible gas as in a conventional generator. Gas comes to the surface through the second well.

Producer gas is widely used for heating industrial furnaces - metallurgical, coke ovens and as fuel in cars (Fig. 4).

Rice. 3. Scheme of underground gasification of coal.

A number of organic products, such as liquid fuel, are synthesized from hydrogen and carbon monoxide in water gas. Synthetic liquid fuel is a fuel (mainly gasoline) obtained by synthesis from carbon monoxide and hydrogen at 150-170 degrees Celsius and a pressure of 0.7 - 20 MN/m2 (200 kgf/cm2), in the presence of a catalyst (nickel, iron, cobalt ). The first production of synthetic liquid fuel was organized in Germany during the 2nd World War due to a shortage of oil. Synthetic liquid fuel has not become widespread due to its high cost. Water gas is used to produce hydrogen. To do this, water gas mixed with water vapor is heated in the presence of a catalyst and as a result, hydrogen is obtained in addition to that already present in the water gas: CO + H 2 O = CO 2 + H 2

5. THERMAL BALANCE OF COMBUSTION

Let us consider methods for calculating the heat balance of the combustion process of gaseous, liquid and solid fuels. The calculation comes down to solving the following problems.

· Determination of the heat of combustion (calorific value) of fuel.

· Determination of theoretical combustion temperature.

5.1. HEAT OF COMBUSTION

Chemical reactions are accompanied by the release or absorption of heat. When heat is released, the reaction is called exothermic, and when heat is absorbed, it is called endothermic. All combustion reactions are exothermic, and combustion products are exothermic compounds.

Released (or absorbed) during flow chemical reaction heat is called the heat of reaction. In exothermic reactions it is positive, in endothermic reactions it is negative. The combustion reaction is always accompanied by the release of heat. Heat of combustion Q g(J/mol) is the amount of heat that is released during the complete combustion of one mole of a substance and the transformation of a combustible substance into products of complete combustion. The mole is the basic SI unit of quantity of a substance. One mole is the amount of substance that contains the same number of particles (atoms, molecules, etc.) as there are atoms in 12 g of the carbon-12 isotope. The mass of an amount of substance equal to 1 mole (molecular or molar mass) numerically coincides with the relative molecular mass of a given substance.

For example, the relative molecular weight of oxygen (O 2) is 32, carbon dioxide (CO 2) is 44, and the corresponding molecular weights will be M = 32 g/mol and M = 44 g/mol. Thus, one mole of oxygen contains 32 grams of this substance, and one mole of CO 2 contains 44 grams of carbon dioxide.

In technical calculations, it is not the heat of combustion that is most often used. Q g, and the calorific value of the fuel Q(J/kg or J/m 3). The calorific value of a substance is the amount of heat that is released during complete combustion of 1 kg or 1 m 3 of a substance. For liquid and solid substances, the calculation is carried out per 1 kg, and for gaseous substances - per 1 m 3.

Knowledge of the heat of combustion and calorific value of the fuel is necessary to calculate the combustion or explosion temperature, explosion pressure, flame propagation speed and other characteristics. The calorific value of the fuel is determined either experimentally or by calculation. When experimentally determining the calorific value, a given mass of solid or liquid fuel is burned in a calorimetric bomb, and in the case of gaseous fuel, in a gas calorimeter. These instruments measure the total heat Q 0 released during combustion of a sample of fuel weighing m. Calorific value Q g is found by the formula

The relationship between the heat of combustion and
calorific value of fuel

To establish a connection between the heat of combustion and the calorific value of a substance, it is necessary to write down the equation for the chemical reaction of combustion.

The product of complete combustion of carbon is carbon dioxide:

C+O2 →CO2.

The product of complete combustion of hydrogen is water:

2H 2 +O 2 →2H 2 O.

The product of complete combustion of sulfur is sulfur dioxide:

S +O 2 →SO 2.

In this case, nitrogen, halogens and other non-combustible elements are released in free form.

Combustible substance - gas

As an example, let us calculate the calorific value of methane CH 4, for which the heat of combustion is equal to Q g=882.6 .

· Let's determine the molecular weight of methane in accordance with its chemical formula(CH 4):

M=1∙12+4∙1=16 g/mol.

· Let's determine the calorific value of 1 kg of methane:

· Let's find the volume of 1 kg of methane, knowing its density ρ=0.717 kg/m3 under normal conditions:

· Let's determine the calorific value of 1 m 3 of methane:

The calorific value of any combustible gases is determined similarly. For many common substances, heat of combustion and calorific values have been measured with high accuracy and are given in the relevant reference literature. Here is a table of the calorific values of some gaseous substances (Table 5.1). Magnitude Q in this table is given in MJ/m 3 and in kcal/m 3, since 1 kcal = 4.1868 kJ is often used as a unit of heat.

Table 5.1

Calorific value gaseous fuels

Substance			Acetylene
Q
Q

A flammable substance is a liquid or solid

As an example, let us calculate the calorific value of ethyl alcohol C 2 H 5 OH, for which the heat of combustion is Q g= 1373.3 kJ/mol.

· Let's determine the molecular weight of ethyl alcohol in accordance with its chemical formula (C 2 H 5 OH):

M = 2∙12 + 5∙1 + 1∙16 + 1∙1 = 46 g/mol.

Let's determine the calorific value of 1 kg of ethyl alcohol:

The calorific value of any liquid and solid combustibles is determined similarly. In table 5.2 and 5.3 show the calorific values Q(MJ/kg and kcal/kg) for some liquids and solids.

Table 5.2

Calorific value liquid fuels

Substance	Methyl alcohol	Ethanol	Fuel oil, oil
Q
Q

Table 5.3

Calorific value of solid fuels

Substance	The tree is fresh	Dry wood	Brown coal	Dry peat	Anthracite, coke
Q
Q

Mendeleev's formula

If the calorific value of the fuel is unknown, then it can be calculated using the empirical formula proposed by D.I. Mendeleev. To do this, you need to know the elemental composition of the fuel (fuel equivalent formula), that is, the percentage content of the following elements in it:

Oxygen (O);

Hydrogen (H);

Carbon (C);

Sulfur (S);

Ashes (A);

Water (W).

Fuel combustion products always contain water vapor, formed both due to the presence of moisture in the fuel and during the combustion of hydrogen. Waste combustion products leave an industrial plant at a temperature above the dew point. Therefore, the heat that is released during the condensation of water vapor cannot be usefully used and should not be taken into account in thermal calculations.

The net calorific value is usually used for calculation Q n fuel, which takes into account heat losses with water vapor. For solid and liquid fuels the value Q n(MJ/kg) is approximately determined by the Mendeleev formula:

Q n=0.339+1.025+0.1085 – 0.1085 – 0.025, (5.1)

where the percentage (wt.%) content of the corresponding elements in the fuel composition is indicated in parentheses.

This formula takes into account the heat of exothermic combustion reactions of carbon, hydrogen and sulfur (with a plus sign). Oxygen included in the fuel partially replaces oxygen in the air, so the corresponding term in formula (5.1) is taken with a minus sign. When moisture evaporates, heat is consumed, so the corresponding term containing W is also taken with a minus sign.

A comparison of calculated and experimental data on the calorific value of different fuels (wood, peat, coal, oil) showed that calculation using the Mendeleev formula (5.1) gives an error not exceeding 10%.

Net calorific value Q n(MJ/m3) of dry combustible gases can be calculated with sufficient accuracy as the sum of the products of the calorific value of individual components and their percentage content in 1 m3 of gaseous fuel.

Q n= 0.108[Н 2 ] + 0.126[СО] + 0.358[СН 4 ] + 0.5[С 2 Н 2 ] + 0.234[Н 2 S ]…, (5.2)

where the percentage (volume %) content of the corresponding gases in the mixture is indicated in parentheses.

On average, the calorific value of natural gas is approximately 53.6 MJ/m 3 . In artificially produced combustible gases, the content of methane CH4 is insignificant. The main flammable components are hydrogen H2 and carbon monoxide CO. In coke oven gas, for example, the H2 content reaches (55 ÷ 60)%, and the lower calorific value of such gas reaches 17.6 MJ/m3. The generator gas contains CO ~ 30% and H 2 ~ 15%, while the lower calorific value of the generator gas is Q n= (5.2÷6.5) MJ/m3. The content of CO and H 2 in blast furnace gas is lower; magnitude Q n= (4.0÷4.2) MJ/m 3.

Let's look at examples of calculating the calorific value of substances using the Mendeleev formula.

Let us determine the calorific value of coal, the elemental composition of which is given in table. 5.4.

Table 5.4

Elemental composition of coal

· Let's substitute those given in the table. 5.4 data in the Mendeleev formula (5.1) (nitrogen N and ash A are not included in this formula, since they are inert substances and do not participate in the combustion reaction):

Q n=0.339∙37.2+1.025∙2.6+0.1085∙0.6–0.1085∙12–0.025∙40=13.04 MJ/kg.

Let us determine the amount of firewood required to heat 50 liters of water from 10° C to 100° C, if 5% of the heat released during combustion is consumed for heating, and the heat capacity of water With=1 kcal/(kg∙deg) or 4.1868 kJ/(kg∙deg). The elemental composition of firewood is given in table. 5.5:

Table 5.5

Elemental composition of firewood

· Let's find the calorific value of firewood using the Mendeleev formula (5.1):

Q n=0.339∙43+1.025∙7–0.1085∙41–0.025∙7= 17.12 MJ/kg.

· Let's determine the amount of heat spent on heating water when burning 1 kg of firewood (taking into account the fact that 5% of the heat (a = 0.05) released during combustion is spent on heating it):

Q 2 =a Q n=0.05·17.12=0.86 MJ/kg.

· Let's determine the amount of firewood required to heat 50 liters of water from 10° C to 100° C:

kg.

Thus, about 22 kg of firewood is required to heat water.

Classification of flammable gases

For gas supply to cities and industrial enterprises They use various flammable gases that differ in origin, chemical composition and physical properties.

Based on their origin, combustible gases are divided into natural, or natural, and artificial, produced from solid and liquid fuels.

Natural gases extracted from wells cleanly gas fields or oil fields along with oil. Gases from oil fields are called associated gases.

Gases from pure gas fields mainly consist of methane with a small content of heavy hydrocarbons. They are characterized by a constant composition and calorific value.

Associated gases Along with methane, they contain a significant amount of heavy hydrocarbons (propane and butane). The composition and calorific value of these gases vary widely.

Artificial gases are produced at special gas plants - or obtained as by-product when burning coal in metallurgical plants, as well as in oil refining plants.

Gases produced from coal are used in our country for urban gas supply in very limited quantities, and their specific gravity is constantly decreasing. At the same time, the production and consumption of liquefied hydrocarbon gases obtained from associated petroleum gases at gas-gasoline plants and at oil refineries during oil refining is growing. Liquid hydrocarbon gases used for municipal gas supply consist mainly of propane and butane.

Composition of gases

The type of gas and its composition largely determine the scope of gas application, the layout and diameters of the gas network, constructive solutions gas burner devices and individual gas pipeline units.

Gas consumption depends on the calorific value, and hence the diameters of gas pipelines and gas combustion conditions. When using gas in industrial installations, the combustion temperature and flame propagation speed and the constancy of the composition of the gas fuel are very important. Composition of gases, as well as physical and chemical properties They primarily depend on the type and method of obtaining gases.

Combustible gases are mechanical mixtures of various gases<как горючих, так и негорючих.

The combustible part of gaseous fuel includes: hydrogen (H 2) - a colorless, taste and odorless gas, its lower calorific value is 2579 kcal/nm 3\ methane (CH 4) - a gas without color, taste and smell, is the main combustible part of natural gases, its lower calorific value is 8555 kcal/nm 3 ; carbon monoxide (CO) - a colorless, tasteless and odorless gas, produced by incomplete combustion of any fuel, very toxic, lower calorific value 3018 kcal/nm 3 ; heavy-hydrocarbons (S p N t), This name<и формулой обозначается целый ряд углеводородов (этан - С2Н 6 , пропан - С 3 Нв, бутан- С4Н 10 и др.), низшая теплотворная способность этих газов колеблется от 15226 до 34890 kcal/nm*.

The non-combustible part of gaseous fuel includes: carbon dioxide (CO 2), oxygen (O 2) and nitrogen (N 2).

The non-combustible part of gases is usually called ballast. Natural gases are characterized by high calorific value and a complete absence of carbon monoxide. At the same time, a number of deposits, mainly gas and oil, contain a very toxic (and corrosive) gas - hydrogen sulfide (H 2 S). Most artificial coal gases contain a significant amount of highly toxic gas - carbon monoxide (CO). The presence of oxides in the gas carbon and other toxic substances are highly undesirable, since they complicate operational work and increase the danger when using gas. In addition to the main components, the composition of gases includes various impurities, the specific value of which is negligible. However, if you consider that thousands of gases are supplied through gas pipelines. even millions of cubic meters of gas, then the total amount of impurities reaches a significant value. Many impurities fall out in gas pipelines, which ultimately leads to a decrease in their throughput, and sometimes to a complete cessation of gas passage. Therefore, the presence of impurities in gas must be taken into account when designing gas pipelines. , and during operation.

The amount and composition of impurities depend on the method of gas production or extraction and the degree of its purification. The most harmful impurities are dust, tar, naphthalene, moisture and sulfur compounds.

Dust appears in gas during the production process (extraction) or during gas transportation through pipelines. Resin is a product of thermal decomposition of fuel and accompanies many artificial gases. If there is dust in the gas, the resin contributes to the formation of tar-mud plugs and blockages of gas pipelines.

Naphthalene is commonly found in man-made coal gases. At low temperatures, naphthalene precipitates in pipes and, together with other solid and liquid impurities, reduces the flow area of gas pipelines.

Moisture in the form of vapor is contained in almost all natural and artificial gases. It gets into natural gases in the gas field itself due to contacts of gases with the surface of water, and artificial gases are saturated with water during the production process. The presence of moisture in gas in significant quantities is undesirable, since it reduces the calorific value of the gas. In addition, it has a high heat capacity of vaporization , moisture during gas combustion carries away a significant amount of heat along with combustion products into the atmosphere. A high moisture content in the gas is also undesirable because, condensing when the gas is cooled during its movement through the pipes, it can create water plugs in the gas pipeline (at lower levels). points) that need to be deleted. This requires the installation of special condensate collectors and pumping them out.

Sulfur compounds, as already noted, include hydrogen sulfide, as well as carbon disulfide, mercaptan, etc. These compounds not only have a harmful effect on human health, but also cause significant corrosion of pipes.

Other harmful impurities include ammonia and cyanide compounds, which are found mainly in coal gases. The presence of ammonia and cyanide compounds leads to increased corrosion of pipe metal.

The presence of carbon dioxide and nitrogen in flammable gases is also undesirable. These gases do not participate in the combustion process, acting as ballast that reduces the calorific value, which leads to an increase in the diameter of gas pipelines and a decrease in the economic efficiency of using gaseous fuel.

The composition of gases used for urban gas supply must meet the requirements of GOST 6542-50 (Table 1).

Table 1

The average values of the composition of natural gases from the most famous fields in the country are presented in table. 2.

From gas fields (dry)

Western Ukraine. . .	81,2	7,5	4,5	3,7	2,5	- .	0,1	0,5	0,735
Shebelinskoe.........................................	92,9	4,5	0,8	0,6	0,6	____ .	0,1	0,5	0,603
Stavropol region. .	98,6	0,4	0,14	0,06		-	0,1	0,7	0,561
Krasnodar region. .	92,9		0,5	-	0,5	_	0,01	0,09	0,595
Saratovskoe...............................	93,4	2,1	0,8	0,4	0,3	Traces	0,3	2,7	0,576
Gazli, Bukhara region	96,7		0,35	0,4"			0,1	0,45	0,575
From gas and oil fields (associated)
Romashkino...............................			18,5	6,2	4,7		0,1	11,5	1,07
				7,4	4,6	____	Traces		1,112	__ .
Tuymazy.........................			18,4	6,8	4,6	____	0,1	7,1	1,062	-
Ashy......		23,5		9,3	3,5	____	0,2	4,5	1,132	-
Fat........ ................................ .				2,5		. ___ .		1,5	0,721	-
Syzran-neft...................................	31,9	23,9 -	5,9	2,7	0,8	1,7	1,6	31,5	0,932	-
Ishimbay...................................	42,4		20,5	7,2	3,1	2,8			1,040	_
Andijan. ...............................	66,5	16,6	9,4	3,1	3,1	0,03	0,2	4,17	0,801 ;

Calorific value of gases

The amount of heat released during complete combustion of a unit amount of fuel is called calorific value (Q) or, as is sometimes said, calorific value, or calorific value, which is one of the main characteristics of fuel.

The calorific value of gases is usually referred to as 1 m 3, taken under normal conditions.

In technical calculations, normal conditions mean the state of the gas at a temperature of 0°C and, at a pressure of 760 mmHg Art. The volume of gas under these conditions is denoted nm 3(normal cubic meter).

For industrial gas measurements according to GOST 2923-45, temperature 20°C and Pressure 760 are taken as normal conditions mmHg Art. The volume of gas assigned to these conditions, as opposed to nm 3 we'll call m 3 (cubic meter).

Calorific value of gases (Q)) expressed in kcal/nm e or in kcal/m3.

For liquefied gases, the calorific value is referred to as 1 kg.

There are higher (Qc) and lower (Qn) calorific values. Gross calorific value takes into account the heat of condensation of water vapor generated during fuel combustion. The lower calorific value does not take into account the heat contained in the water vapor of the combustion products, since the water vapor does not condense, but is carried away with the combustion products.

The concepts Q in and Q n refer only to those gases whose combustion releases water vapor (these concepts do not apply to carbon monoxide, which does not produce water vapor upon combustion).

When water vapor condenses, heat is released equal to 539 kcal/kg. In addition, when the condensate is cooled to 0°C (or 20°C), heat is released in the amount of 100 or 80, respectively. kcal/kg.

In total, more than 600 heat is released due to the condensation of water vapor. kcal/kg, which is the difference between the higher and lower calorific value of the gas. For most gases used in urban gas supply, this difference is 8-10%.

The calorific values of some gases are given in table. 3.

For urban gas supply, gases are currently used that, as a rule, have a calorific value of at least 3500 kcal/nm 3 . This is explained by the fact that in urban areas gas is supplied through pipes over considerable distances. When the calorific value is low, a large quantity must be supplied. This inevitably leads to an increase in the diameters of gas pipelines and, as a consequence, to an increase in metal investments and funds for the construction of gas networks, and subsequently to an increase in operating costs. A significant disadvantage of low-calorie gases is that in most cases they contain a significant amount of carbon monoxide, which increases the danger when using gas, as well as when servicing networks and installations.

Gas calorific value less than 3500 kcal/nm 3 most often used in industry, where it is not necessary to transport it over long distances and it is easier to organize combustion. For urban gas supply, it is desirable to have a constant calorific value of gas. Fluctuations, as we have already established, are allowed no more than 10%. A larger change in the calorific value of gas requires new adjustments, and sometimes the replacement of a large number of standardized burners of household appliances, which is associated with significant difficulties.

The calorific value of gases is usually referred to as 1 m 3, taken under normal conditions.

Calorific value of gases (Q)) expressed in kcal/nm e or in kcal/m3.

For liquefied gases, the calorific value is referred to as 1 kg.

The concepts Q in and Q n refer only to those gases whose combustion releases water vapor (these concepts do not apply to carbon monoxide, which does not produce water vapor upon combustion).

The calorific values of some gases are given in table. 3.