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. Quantity gas fuel expressed in cubic meters under normal conditions (760 mm Hg 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 is a product of petroleum refining - it 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 P 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
		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 DE boilers no less than 189 rubles per ton of steam.

DKVR type boilers consume from 103 to 118 m3 of natural gas to produce one ton of steam. Minimum estimated cost tons 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 area 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. lower limit The explosiveness of natural gases ranges from 3% to 6%, and the top - 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 gases are colorless (invisible) and odorless, which makes them dangerous if they penetrate into interior space 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 gasifying 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.

Gasification process solid fuel shown on laboratory experience(Fig. 1).

Having filled the refractory tube with pieces of charcoal, we heat it strongly and let oxygen pass through from the gasometer. Let's 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 it 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 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 produced for a long time, since the reaction of its formation is endothermic (with the absorption of heat), and therefore the fuel in the generator cools down. To maintain the coal in a hot state, 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. Recently, steam-oxygen blast has become widely used for fuel gasification. Simultaneous blowing of water vapor and oxygen through the fuel layer allows the process to run continuously, significantly increasing the productivity of the generator and producing gas with a high content of hydrogen and carbon monoxide. Modern gas generators are

powerful devices continuous action. So that when supplying fuel to the gas generator, combustible and

poisonous gases

did not penetrate into the atmosphere, 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.

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 ignited 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 flammable 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 and as fuel in cars (Fig. 4).

Rice. 3. Scheme of underground gasification of coal.

A series of compounds is synthesized from hydrogen and carbon monoxide in water gas organic products, for example liquid fuel. 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 ). First production of synthetic liquid fuel 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

Substances of organic origin include fuels that, when burned, release a certain amount of thermal energy. Heat production must be characterized by high efficiency and absence of side effects, in particular, substances harmful to human health and the environment.

For ease of loading into the firebox wood material cut into individual elements up to 30 cm long. To increase the efficiency of their use, the firewood should be as dry as possible, and the burning process should be relatively slow. In many respects, firewood from such types is suitable for heating premises. hardwood, like oak and birch, hazel and ash, hawthorn. Due to the high resin content, increased speed combustion and low calorific value coniferous trees in this regard they are significantly inferior.

It should be understood that the value of the calorific value is affected by the density of wood.

This natural material plant origin, extracted from sedimentary rock.

This type of solid fuel contains carbon and other chemical elements. There is a division of material into types depending on its age. Brown coal is considered the youngest, followed by hard coal, and anthracite is older than all other types. The age of a combustible substance also determines its moisture content, which is more present in young material.

During the combustion of coal, environmental pollution occurs, and slag is formed on the boiler grates, which to a certain extent creates an obstacle to normal combustion. The presence of sulfur in the material is also an unfavorable factor for the atmosphere, since in the air space this element is converted into sulfuric acid.

However, consumers should not fear for their health. Manufacturers of this material, taking care of private customers, strive to reduce the sulfur content in it. The heating value of coal can vary even within the same type. The difference depends on the characteristics of the subspecies and the content in it minerals, as well as the geography of production. As a solid fuel, not only pure coal is found, but also low-enriched coal slag, pressed into briquettes.

Pellets (fuel granules) are solid fuels created industrially from wood and plant waste: shavings, bark, cardboard, straw.

The raw material, crushed to dust, is dried and poured into a granulator, from where it comes out in the form of granules a certain shape. To add viscosity to the mass, a plant polymer, lignin, is used. Complexity production process and high demand determine the cost of pellets. The material is used in specially equipped boilers.

Types of fuel are determined depending on the material from which they are processed:

• round timber of trees of any species;
• straw;
• peat;
• sunflower husk.

Among the advantages that they have fuel pellets, it is worth noting the following qualities:

• environmental friendliness;
• inability to deform and resistance to fungus;
• easy storage even outdoors;
• uniformity and duration of combustion;
• relatively low cost;
• Possibility of use for various heating devices;
• suitable granule size for automatic download into a specially equipped boiler.

Briquettes

Briquettes are solid fuels that are in many ways similar to pellets. For their manufacture, identical materials are used: wood chips, shavings, peat, husks and straw. During the production process, raw materials are crushed and formed into briquettes by compression. This material is also environmentally friendly clean fuel. It is convenient to store even on outdoors. Smooth, uniform and slow combustion of this fuel can be observed both in fireplaces and stoves, and in heating boilers.

The types of environmentally friendly solid fuel discussed above are a good alternative for generating heat. In comparison with fossil sources of thermal energy, which have an unfavorable effect on combustion environment and are, in addition, non-renewable, alternative fuel has clear advantages and a relatively low cost, which is important for certain categories of consumers.

At the same time, the fire hazard of such fuels is much higher. Therefore, it is necessary to take some safety measures regarding their storage and the use of fire-resistant materials for walls.

Liquid and gaseous fuels

As for liquid and gaseous flammable substances, the situation here is as follows.

The tables show the mass specific heat combustion of fuel (liquid, solid and gaseous) and some other combustible materials. The following fuels were considered: coal, firewood, coke, peat, kerosene, oil, alcohol, gasoline, natural gas, etc.

List of tables:

During an exothermic fuel oxidation reaction, it chemical energy becomes thermal with the release of a certain amount of heat. The resulting thermal energy is usually called the heat of combustion of fuel. It depends on its chemical composition, humidity and is the main one. The heat of combustion of fuel per 1 kg of mass or 1 m 3 of volume forms the mass or volumetric specific heat of combustion.

The specific heat of combustion of a fuel is the amount of heat released when complete combustion unit of mass or volume of solid, liquid or gaseous fuel. In the International System of Units, this value is measured in J/kg or J/m 3.

The specific heat of combustion of a fuel can be determined experimentally or calculated analytically. Experimental methods definitions calorific value based on practical dimension the amount of heat released when a fuel burns, for example in a calorimeter with a thermostat and a combustion bomb. For fuel with a known chemical composition, the specific heat of combustion can be determined using the periodic formula.

There are higher and lower specific heats of combustion. The higher calorific value is maximum number the heat released during complete combustion of the fuel, taking into account the heat expended on the evaporation of moisture contained in the fuel. Net calorific value less than value higher by the amount of heat of condensation, which is formed from the moisture of the fuel and hydrogen of the organic mass, which turns into water during combustion.

To determine fuel quality indicators, as well as thermotechnical calculations usually use lower specific heat of combustion, which is the most important thermal and performance characteristics fuel and is shown in the tables below.

Specific heat of combustion of solid fuels (coal, firewood, peat, coke)

The table presents the values ​​of the specific heat of combustion of dry solid fuel in the dimension MJ/kg. Fuel in the table is arranged by name in alphabetical order.

Of the solid fuels considered, coking coal has the highest calorific value - its specific heat of combustion is 36.3 MJ/kg (or in SI units 36.3·10 6 J/kg). In addition, high heat of combustion is characteristic of coal, anthracite, charcoal and brown coal.

Fuels with low energy efficiency include wood, firewood, gunpowder, milling peat, and oil shale. For example, the specific heat of combustion of firewood is 8.4...12.5, and that of gunpowder is only 3.8 MJ/kg.

Specific heat of combustion of solid fuels (coal, firewood, peat, coke)

Fuel
Anthracite	26,8…34,8
Wood pellets (pellets)	18,5
Dry firewood	8,4…11
Dry birch firewood	12,5
Gas coke	26,9
Blast coke	30,4
Semi-coke	27,3
Powder	3,8
Slate	4,6…9
Oil shale	5,9…15
Solid rocket fuel	4,2…10,5
Peat	16,3
Fibrous peat	21,8
Milled peat	8,1…10,5
Peat crumb	10,8
Brown coal	13…25
Brown coal (briquettes)	20,2
Brown coal (dust)	25
Donetsk coal	19,7…24
Charcoal	31,5…34,4
Coal	27
Coking coal	36,3
Kuznetsk coal	22,8…25,1
Chelyabinsk coal	12,8
Ekibastuz coal	16,7
Frestorf	8,1
Slag	27,5

Specific heat of combustion of liquid fuels (alcohol, gasoline, kerosene, oil)

A table is given of the specific heat of combustion of liquid fuel and some other organic liquids. It should be noted that fuels such as gasoline, diesel fuel and oil have high heat release during combustion.

The specific heat of combustion of alcohol and acetone is significantly lower than traditional motor fuels. In addition, liquid rocket fuel has a relatively low calorific value and, with complete combustion of 1 kg of these hydrocarbons, an amount of heat will be released equal to 9.2 and 13.3 MJ, respectively.

Specific heat of combustion of liquid fuels (alcohol, gasoline, kerosene, oil)

Fuel	Specific heat of combustion, MJ/kg
Acetone	31,4
Gasoline A-72 (GOST 2084-67)	44,2
Aviation gasoline B-70 (GOST 1012-72)	44,1
Gasoline AI-93 (GOST 2084-67)	43,6
Benzene	40,6
Winter diesel fuel (GOST 305-73)	43,6
Summer diesel fuel (GOST 305-73)	43,4
Liquid rocket fuel (kerosene + liquid oxygen)	9,2
Aviation kerosene	42,9
Kerosene for lighting (GOST 4753-68)	43,7
Xylene	43,2
High sulfur fuel oil	39
Low sulfur fuel oil	40,5
Low-sulfur fuel oil	41,7
Sulphurous fuel oil	39,6
Methyl alcohol (methanol)	21,1
n-Butyl alcohol	36,8
Oil	43,5…46
Methane oil	21,5
Toluene	40,9
White spirit (GOST 313452)	44
Ethylene glycol	13,3
Ethyl alcohol (ethanol)	30,6

Specific heat of combustion of gaseous fuels and combustible gases

A table is presented of the specific heat of combustion of gaseous fuel and some other combustible gases in the dimension MJ/kg. Of the gases considered, it has the highest mass specific heat of combustion. The complete combustion of one kilogram of this gas will release 119.83 MJ of heat. Also, fuel such as natural gas has a high calorific value - the specific heat of combustion of natural gas is 41...49 MJ/kg (for pure gas it is 50 MJ/kg).

Specific heat of combustion of gaseous fuel and combustible gases (hydrogen, natural gas, methane)

Fuel	Specific heat of combustion, MJ/kg
1-Butene	45,3
Ammonia	18,6
Acetylene	48,3
Hydrogen	119,83
Hydrogen, mixture with methane (50% H 2 and 50% CH 4 by weight)	85
Hydrogen, mixture with methane and carbon monoxide (33-33-33% by weight)	60
Hydrogen, mixture with carbon monoxide (50% H 2 50% CO 2 by weight)	65
Blast furnace gas	3
Coke Oven Gas	38,5
Liquefied hydrocarbon gas LPG (propane-butane)	43,8
Isobutane	45,6
Methane	50
n-Butane	45,7
n-Hexane	45,1
n-Pentane	45,4
Associated gas	40,6…43
Natural gas	41…49
Propadiene	46,3
Propane	46,3
Propylene	45,8
Propylene, mixture with hydrogen and carbon monoxide (90%-9%-1% by weight)	52
Ethane	47,5
Ethylene	47,2

Specific heat of combustion of some combustible materials

A table is provided of the specific heat of combustion of some combustible materials (wood, paper, plastic, straw, rubber, etc.). Materials with high heat release during combustion should be noted. These materials include: rubber various types, expanded polystyrene (foam), polypropylene and polyethylene.

Specific heat of combustion of some combustible materials

Fuel	Specific heat of combustion, MJ/kg
Paper	17,6
Leatherette	21,5
Wood (bars with 14% moisture content)	13,8
Wood in stacks	16,6
Oak wood	19,9
Spruce wood	20,3
Wood green	6,3
Pine wood	20,9
Capron	31,1
Carbolite products	26,9
Cardboard	16,5
Styrene butadiene rubber SKS-30AR	43,9
Natural rubber	44,8
Synthetic rubber	40,2
Rubber SKS	43,9
Chloroprene rubber	28
Polyvinyl chloride linoleum	14,3
Double-layer polyvinyl chloride linoleum	17,9
Polyvinyl chloride linoleum on a felt basis	16,6
Warm-based polyvinyl chloride linoleum	17,6
Fabric-based polyvinyl chloride linoleum	20,3
Rubber linoleum (Relin)	27,2
Paraffin paraffin	11,2
Polystyrene foam PVC-1	19,5
Foam plastic FS-7	24,4
Foam plastic FF	31,4
Expanded polystyrene PSB-S	41,6
Polyurethane foam	24,3
Fiberboard	20,9
Polyvinyl chloride (PVC)	20,7
Polycarbonate	31
Polypropylene	45,7
Polystyrene	39
High pressure polyethylene	47
Low-pressure polyethylene	46,7
Rubber	33,5
Ruberoid	29,5
Channel soot	28,3
Hay	16,7
Straw	17
Organic glass (plexiglass)	27,7
Textolite	20,9
Tol	16
TNT	15
Cotton	17,5
Cellulose	16,4
Wool and wool fibers	23,1

Sources:

1. GOST 147-2013 Solid mineral fuel. Determination of the higher calorific value and calculation of the lower calorific value.
2. GOST 21261-91 Petroleum products. Method for determining the higher calorific value and calculating the lower calorific value.
3. GOST 22667-82 Natural flammable gases. Calculation method for determining the calorific value, relative density and Wobbe number.
4. GOST 31369-2008 Natural gas. Calculation of calorific value, density, relative density and Wobbe number based on component composition.
5. Zemsky G. T. Flammable properties of inorganic and organic materials: reference book M.: VNIIPO, 2016 - 970 p.

The heat of combustion is determined by the chemical composition of the combustible substance. The chemical elements contained in a flammable substance are indicated by accepted symbols WITH , N , ABOUT , N , S, and ash and water are symbols A And W respectively.

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  The heat of combustion can be related to the working mass of the combustible substance Q P (\displaystyle Q^(P)), that is, to the flammable substance in the form in which it reaches the consumer; to the dry weight of the substance Q C (\displaystyle Q^(C)); to a flammable mass of substance Q Γ (\displaystyle Q^(\Gamma )), that is, to a flammable substance that does not contain moisture and ash.

  There are higher ( Q B (\displaystyle Q_(B))) and lower ( Q H (\displaystyle Q_(H))) heat of combustion.

  Under higher calorific value understand the amount of heat that is released during complete combustion of a substance, including the heat of condensation of water vapor when cooling the combustion products.

  Net calorific value corresponds to the amount of heat that is released during complete combustion, without taking into account the heat of condensation of water vapor. The heat of condensation of water vapor is also called latent heat of vaporization (condensation).

  The lower and higher calorific values ​​are related by the relation: Q B = Q H + k (W + 9 H) (\displaystyle Q_(B)=Q_(H)+k(W+9H)),

  where k is a coefficient equal to 25 kJ/kg (6 kcal/kg); W is the amount of water in the flammable substance, % (by mass); H is the amount of hydrogen in a combustible substance, % (by mass).

  Calculation of calorific value

  Thus, the higher calorific value is the amount of heat released during complete combustion of a unit mass or volume (for gas) of a combustible substance and cooling of the combustion products to the dew point temperature. In thermal engineering calculations, the higher calorific value is taken as 100%. The latent heat of combustion of a gas is the heat that is released during the condensation of water vapor contained in the combustion products. Theoretically, it can reach 11%.

  In practice, it is not possible to cool combustion products until complete condensation, and therefore the concept of lower calorific value (QHp) has been introduced, which is obtained by subtracting from the higher calorific value the heat of vaporization of water vapor both contained in the substance and those formed during its combustion. The vaporization of 1 kg of water vapor requires 2514 kJ/kg (600 kcal/kg). The lower calorific value is determined by the formulas (kJ/kg or kcal/kg):

  Q H P = Q B P − 2514 ⋅ ((9 H P + W P) / 100) (\displaystyle Q_(H)^(P)=Q_(B)^(P)-2514\cdot ((9H^(P)+W^ (P))/100))(for solid matter)

  Q H P = Q B P − 600 ⋅ ((9 H P + W P) / 100) (\displaystyle Q_(H)^(P)=Q_(B)^(P)-600\cdot ((9H^(P)+W^ (P))/100))(For liquid substance), Where:

  2514 - heat of vaporization at 0 °C and atmospheric pressure, kJ/kg;

  H P (\displaystyle H^(P)) And W P (\displaystyle W^(P))- content of hydrogen and water vapor in the working fuel, %;

  9 is a coefficient showing that the combustion of 1 kg of hydrogen in combination with oxygen produces 9 kg of water.

  Heat of combustion is the most important characteristic fuel, as it determines the amount of heat obtained by burning 1 kg of solid or liquid fuel or 1 m³ of gaseous fuel in kJ/kg (kcal/kg). 1 kcal = 4.1868 or 4.19 kJ.

  The lower calorific value is determined experimentally for each substance and is a reference value. It can also be determined for solid and liquid materials, with a known elemental composition, by calculation method in accordance with the formula of D. I. Mendeleev, kJ/kg or kcal/kg:

  Q H P = 339 ⋅ C P + 1256 ⋅ H P − 109 ⋅ (O P − S L P) − 25.14 ⋅ (9 ⋅ H P + W P) (\displaystyle Q_(H)^(P)=339\cdot C^(P)+1256\ cdot H^(P)-109\cdot (O^(P)-S_(L)^(P))-25.14\cdot (9\cdot H^(P)+W^(P)))

  Q H P = 81 ⋅ C P + 246 ⋅ H P − 26 ⋅ (O P + S L P) − 6 ⋅ W P (\displaystyle Q_(H)^(P)=81\cdot C^(P)+246\cdot H^(P) -26\cdot (O^(P)+S_(L)^(P))-6\cdot W^(P)), Where:

  C P (\displaystyle C_(P)), H P (\displaystyle H_(P)), O P (\displaystyle O_(P)), S L P (\displaystyle S_(L)^(P)), W P (\displaystyle W_(P))- content of carbon, hydrogen, oxygen, volatile sulfur and moisture in the working mass of fuel in% (by weight).

  For comparative calculations, the so-called conventional fuel is used, which has a specific heat of combustion equal to 29308 kJ/kg (7000 kcal/kg).

  In Russia thermal calculations(for example, calculating the heat load to determine the category of the room according to explosion and fire fire danger) are usually carried out according to the lower calorific value, in the USA, Great Britain, France - according to the highest. In the UK and US, before the introduction of the metric system, specific heat of combustion was measured in British thermal units (BTU) per pound (lb) (1Btu/lb = 2.326 kJ/kg).

  Substances and materials	Net calorific value Q H P (\displaystyle Q_(H)^(P)), MJ/kg
  Petrol	41,87
  Kerosene	43,54
  Paper: books, magazines	13,4
  Wood (blocks W = 14%)	13,8
  Natural rubber	44,73
  Polyvinyl chloride linoleum	14,31
  Rubber	33,52
  Staple fiber	13,8
  Polyethylene	47,14
  Expanded polystyrene	41,6
  Cotton loosened	15,7
  Plastic	41,87

  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 of pure 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, contain a significant amount of heavy hydrocarbons (propane and butane). The composition and calorific value of these gases vary widely.

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

  In our country, gases produced from coal are used for urban gas supply in very limited quantities, and specific gravity they are decreasing all the time. 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 urban 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 decisions 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 the speed of flame propagation and the constancy of the composition of the gas fuel are very significant. The composition of gases, as well as their physical and chemical properties, primarily depend on the type and method of obtaining the gases.

  Combustible gases are mechanical mixtures 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 colorless, taste and odorless gas, 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, being 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	Footprints	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	____	Footprints		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 The gas generator device is shown in the figure. It is a steel cylinder with a height of about 5 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, large quantities 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 replacement of a large number of standardized burners of household appliances, which is associated with significant difficulties.